diff --git a/gtk2_ardour/bundle_manager.cc b/gtk2_ardour/bundle_manager.cc
index 42fbabbbe9..04bf240f7c 100644
--- a/gtk2_ardour/bundle_manager.cc
+++ b/gtk2_ardour/bundle_manager.cc
@@ -33,12 +33,16 @@
 BundleEditorMatrix::BundleEditorMatrix (
 	ARDOUR::Session& session, boost::shared_ptr<ARDOUR::Bundle> bundle
 	)
-	: PortMatrix (
-		session, bundle->type(), bundle->ports_are_inputs(),
-		PortGroupList::Mask (PortGroupList::SYSTEM | PortGroupList::OTHER)
-		)
+	: PortMatrix (session, bundle->type(), bundle->ports_are_inputs())
 {
-	_our_bundles.push_back (bundle);
+	_port_group = new PortGroup ("", true);
+	_port_group->bundles.push_back (bundle);
+	_row_ports.push_back (_port_group);
+}
+
+BundleEditorMatrix::~BundleEditorMatrix ()
+{
+	delete _port_group;
 }
 
 void
@@ -89,14 +93,14 @@ BundleEditorMatrix::add_channel (boost::shared_ptr<ARDOUR::Bundle> b)
 		return;
 	}
 
-	_our_bundles.front()->add_channel (d.get_name());
+	_port_group->bundles.front()->add_channel (d.get_name());
 	setup ();
 }
 
 void
 BundleEditorMatrix::remove_channel (boost::shared_ptr<ARDOUR::Bundle> b, uint32_t c)
 {
-	_our_bundles.front()->remove_channel (c);
+	_port_group->bundles.front()->remove_channel (c);
 	setup ();
 }
 
@@ -232,7 +236,10 @@ BundleManager::BundleManager (ARDOUR::Session& session)
 	_tree_view.append_column (_("Name"), _list_model_columns.name);
 	_tree_view.set_headers_visible (false);
 
-	_session.foreach_bundle (sigc::mem_fun (*this, &BundleManager::add_bundle));
+	boost::shared_ptr<ARDOUR::BundleList> bundles = _session.bundles ();
+	for (ARDOUR::BundleList::iterator i = bundles->begin(); i != bundles->end(); ++i) {
+		add_bundle (*i);
+	}
 	
 	/* New / Edit / Delete buttons */
 	Gtk::VBox* buttons = new Gtk::VBox;
diff --git a/gtk2_ardour/bundle_manager.h b/gtk2_ardour/bundle_manager.h
index 1aeb196e67..8ab4279117 100644
--- a/gtk2_ardour/bundle_manager.h
+++ b/gtk2_ardour/bundle_manager.h
@@ -35,6 +35,7 @@ class BundleEditorMatrix : public PortMatrix
 {
   public:
 	BundleEditorMatrix (ARDOUR::Session &, boost::shared_ptr<ARDOUR::Bundle>);
+	~BundleEditorMatrix ();
 
 	void set_state (
 		boost::shared_ptr<ARDOUR::Bundle> ab,
@@ -58,6 +59,9 @@ class BundleEditorMatrix : public PortMatrix
 		return true;
 	}
 	void rename_channel (boost::shared_ptr<ARDOUR::Bundle>, uint32_t);
+
+  private:
+	PortGroup* _port_group;
 };
 
 class BundleEditor : public ArdourDialog
diff --git a/gtk2_ardour/global_port_matrix.cc b/gtk2_ardour/global_port_matrix.cc
index 51b1f47b3f..80ddecc813 100644
--- a/gtk2_ardour/global_port_matrix.cc
+++ b/gtk2_ardour/global_port_matrix.cc
@@ -25,25 +25,19 @@
 #include "ardour/port.h"
 
 GlobalPortMatrix::GlobalPortMatrix (ARDOUR::Session& s, ARDOUR::DataType t)
-	: PortMatrix (s, t, true, PortGroupList::Mask (PortGroupList::BUSS |
-						       PortGroupList::TRACK |
-						       PortGroupList::SYSTEM | 
-						       PortGroupList::OTHER)),
+	: PortMatrix (s, t, true),
 	  _session (s),
-	  _our_port_group_list (s, t, false, PortGroupList::Mask (PortGroupList::BUSS |
-								  PortGroupList::TRACK |
-								  PortGroupList::SYSTEM | 
-								  PortGroupList::OTHER))
+	  _our_port_group_list (t, false)
 {
 	setup ();
 
-	_port_group_list.VisibilityChanged.connect (sigc::mem_fun (*this, &GlobalPortMatrix::group_visibility_changed));
+	_column_ports.VisibilityChanged.connect (sigc::mem_fun (*this, &GlobalPortMatrix::group_visibility_changed));
 }
 
 void
 GlobalPortMatrix::group_visibility_changed ()
 {
-	_our_port_group_list.take_visibility_from (_port_group_list);
+	_row_ports.take_visibility_from (_column_ports);
 	setup ();
 }
 
@@ -51,11 +45,8 @@ GlobalPortMatrix::group_visibility_changed ()
 void
 GlobalPortMatrix::setup ()
 {
-	_our_port_group_list.refresh ();
-	_our_bundles = _our_port_group_list.bundles ();
-	
+	_row_ports.gather (_session);
 	PortMatrix::setup ();
-	
 }
 
 void
diff --git a/gtk2_ardour/io_selector.cc b/gtk2_ardour/io_selector.cc
index d61a37d655..cb1a07ce14 100644
--- a/gtk2_ardour/io_selector.cc
+++ b/gtk2_ardour/io_selector.cc
@@ -42,25 +42,30 @@ using namespace ARDOUR;
 using namespace Gtk;
 
 IOSelector::IOSelector (ARDOUR::Session& session, boost::shared_ptr<ARDOUR::IO> io, bool offer_inputs)
-	: PortMatrix (session, io->default_type(), offer_inputs,
-		      PortGroupList::Mask (PortGroupList::BUSS | 
-					   PortGroupList::SYSTEM | 
-					   PortGroupList::OTHER))
+	: PortMatrix (session, io->default_type(), offer_inputs)
 	, _session (session)
 	, _io (io)
 {
 	/* Listen for ports changing on the IO */
 	_io->PortCountChanged.connect (sigc::hide (mem_fun (*this, &IOSelector::ports_changed)));
+
+	_port_group = new PortGroup ("", true);
+	_row_ports.push_back (_port_group);
 	
 	setup ();
 }
 
+IOSelector::~IOSelector ()
+{
+	delete _port_group;
+}
+
 void
 IOSelector::setup ()
 {
-	_our_bundles.clear ();
-	_our_bundles.push_back (boost::shared_ptr<ARDOUR::Bundle> (new ARDOUR::Bundle));
-	_our_bundles.front()->set_name (_io->name());
+	_port_group->bundles.clear ();
+	_port_group->bundles.push_back (boost::shared_ptr<ARDOUR::Bundle> (new ARDOUR::Bundle));
+	_port_group->bundles.front()->set_name (_io->name());
 
 	if (offering_input ()) {
 		const PortSet& ps (_io->outputs());
@@ -69,8 +74,8 @@ IOSelector::setup ()
 		for (PortSet::const_iterator i = ps.begin(); i != ps.end(); ++i) {
 			char buf[32];
 			snprintf (buf, sizeof(buf), _("out %d"), j + 1);
-			_our_bundles.front()->add_channel (buf);
-			_our_bundles.front()->add_port_to_channel (j, _session.engine().make_port_name_non_relative (i->name()));
+			_port_group->bundles.front()->add_channel (buf);
+			_port_group->bundles.front()->add_port_to_channel (j, _session.engine().make_port_name_non_relative (i->name()));
 			++j;
 		}
 		
@@ -82,8 +87,8 @@ IOSelector::setup ()
 		for (PortSet::const_iterator i = ps.begin(); i != ps.end(); ++i) {
 			char buf[32];
 			snprintf (buf, sizeof(buf), _("in %d"), j + 1);
-			_our_bundles.front()->add_channel (buf);
-			_our_bundles.front()->add_port_to_channel (j, _session.engine().make_port_name_non_relative (i->name()));
+			_port_group->bundles.front()->add_channel (buf);
+			_port_group->bundles.front()->add_port_to_channel (j, _session.engine().make_port_name_non_relative (i->name()));
 			++j;
 		}
 
@@ -303,11 +308,7 @@ IOSelectorWindow::IOSelectorWindow (ARDOUR::Session& session, boost::shared_ptr<
 
 	get_vbox()->set_spacing (8);
 
-	/* XXX: do we still need the ScrolledWindow? */
-	Gtk::ScrolledWindow* sel_scroll = Gtk::manage (new Gtk::ScrolledWindow);
-	sel_scroll->set_policy (Gtk::POLICY_NEVER, Gtk::POLICY_NEVER);
-	sel_scroll->add (_selector);
-	get_vbox()->pack_start (*sel_scroll, true, true);
+	get_vbox()->pack_start (_selector, true, true);
 
 	set_position (Gtk::WIN_POS_MOUSE);
 
diff --git a/gtk2_ardour/io_selector.h b/gtk2_ardour/io_selector.h
index 8b49e5e2de..20bcb2ff27 100644
--- a/gtk2_ardour/io_selector.h
+++ b/gtk2_ardour/io_selector.h
@@ -30,6 +30,7 @@ namespace ARDOUR {
 class IOSelector : public PortMatrix {
   public:
 	IOSelector (ARDOUR::Session&, boost::shared_ptr<ARDOUR::IO>, bool);
+	~IOSelector ();
 
 	void set_state (
 		boost::shared_ptr<ARDOUR::Bundle>,
@@ -62,6 +63,7 @@ class IOSelector : public PortMatrix {
   private:
 	ARDOUR::Session& _session;
 	boost::shared_ptr<ARDOUR::IO> _io;
+	PortGroup* _port_group;
 	
 	void ports_changed ();
 };
diff --git a/gtk2_ardour/mixer_strip.cc b/gtk2_ardour/mixer_strip.cc
index 6f591bc6c0..05f2bb3615 100644
--- a/gtk2_ardour/mixer_strip.cc
+++ b/gtk2_ardour/mixer_strip.cc
@@ -629,11 +629,12 @@ MixerStrip::output_press (GdkEventButton *ev)
 		citems.push_back (MenuElem (_("Disconnect"), mem_fun (*(static_cast<RouteUI*>(this)), &RouteUI::disconnect_output)));
 		citems.push_back (SeparatorElem());
 
-		std::vector<boost::shared_ptr<Bundle> > current = _route->bundles_connected_to_outputs ();
+		ARDOUR::BundleList current = _route->bundles_connected_to_outputs ();
 
- 		_session.foreach_bundle (
-			bind (mem_fun (*this, &MixerStrip::add_bundle_to_output_menu), current)
- 			);
+		boost::shared_ptr<ARDOUR::BundleList> b = _session.bundles ();
+		for (ARDOUR::BundleList::iterator i = b->begin(); i != b->end(); ++i) {
+			add_bundle_to_output_menu (*i, current);
+		}
 
 		output_menu.popup (1, ev->time);
 		break;
@@ -697,11 +698,12 @@ MixerStrip::input_press (GdkEventButton *ev)
 		citems.push_back (MenuElem (_("Disconnect"), mem_fun (*(static_cast<RouteUI*>(this)), &RouteUI::disconnect_input)));
 		citems.push_back (SeparatorElem());
 
-		std::vector<boost::shared_ptr<Bundle> > current = _route->bundles_connected_to_inputs ();
+		ARDOUR::BundleList current = _route->bundles_connected_to_inputs ();
 
-		_session.foreach_bundle (
-			bind (mem_fun (*this, &MixerStrip::add_bundle_to_input_menu), current)
-			);
+		boost::shared_ptr<ARDOUR::BundleList> b = _session.bundles ();
+		for (ARDOUR::BundleList::iterator i = b->begin(); i != b->end(); ++i) {
+			add_bundle_to_input_menu (*i, current);
+		}
 
 		input_menu.popup (1, ev->time);
 		break;
@@ -745,7 +747,7 @@ MixerStrip::bundle_output_chosen (boost::shared_ptr<ARDOUR::Bundle> c)
 }
 
 void
-MixerStrip::add_bundle_to_input_menu (boost::shared_ptr<Bundle> b, std::vector<boost::shared_ptr<Bundle> > const & current)
+MixerStrip::add_bundle_to_input_menu (boost::shared_ptr<Bundle> b, ARDOUR::BundleList const & current)
 {
 	using namespace Menu_Helpers;
 
@@ -770,7 +772,7 @@ MixerStrip::add_bundle_to_input_menu (boost::shared_ptr<Bundle> b, std::vector<b
 }
 
 void
-MixerStrip::add_bundle_to_output_menu (boost::shared_ptr<Bundle> b, std::vector<boost::shared_ptr<Bundle> > const & current)
+MixerStrip::add_bundle_to_output_menu (boost::shared_ptr<Bundle> b, ARDOUR::BundleList const & current)
 {
 	using namespace Menu_Helpers;
 
@@ -833,7 +835,7 @@ MixerStrip::connect_to_pan ()
 void
 MixerStrip::update_input_display ()
 {
-	std::vector<boost::shared_ptr<ARDOUR::Bundle> > c = _route->bundles_connected_to_inputs ();
+	ARDOUR::BundleList c = _route->bundles_connected_to_inputs ();
 
 	/* XXX: how do we represent >1 connected bundle? */
 	if (c.empty() == false) {
@@ -854,7 +856,7 @@ MixerStrip::update_input_display ()
 void
 MixerStrip::update_output_display ()
 {
-	std::vector<boost::shared_ptr<ARDOUR::Bundle> > c = _route->bundles_connected_to_outputs ();
+	ARDOUR::BundleList c = _route->bundles_connected_to_outputs ();
 
 	/* XXX: how do we represent >1 connected bundle? */
 	if (c.empty() == false) {
diff --git a/gtk2_ardour/mixer_strip.h b/gtk2_ardour/mixer_strip.h
index 393a38569e..a831a54117 100644
--- a/gtk2_ardour/mixer_strip.h
+++ b/gtk2_ardour/mixer_strip.h
@@ -180,10 +180,10 @@ class MixerStrip : public RouteUI, public Gtk::EventBox
 	gint output_press (GdkEventButton *);
 
 	Gtk::Menu  input_menu;
-	void add_bundle_to_input_menu (boost::shared_ptr<ARDOUR::Bundle>, std::vector<boost::shared_ptr<ARDOUR::Bundle> > const &);
+	void add_bundle_to_input_menu (boost::shared_ptr<ARDOUR::Bundle>, ARDOUR::BundleList const &);
 
 	Gtk::Menu output_menu;
-	void add_bundle_to_output_menu (boost::shared_ptr<ARDOUR::Bundle>, std::vector<boost::shared_ptr<ARDOUR::Bundle> > const &);
+	void add_bundle_to_output_menu (boost::shared_ptr<ARDOUR::Bundle>, ARDOUR::BundleList const &);
 	
 	void bundle_input_chosen (boost::shared_ptr<ARDOUR::Bundle>);
 	void bundle_output_chosen (boost::shared_ptr<ARDOUR::Bundle>);
diff --git a/gtk2_ardour/port_group.cc b/gtk2_ardour/port_group.cc
index accab1d183..616f674ddb 100644
--- a/gtk2_ardour/port_group.cc
+++ b/gtk2_ardour/port_group.cc
@@ -60,7 +60,7 @@ PortGroup::clear ()
 bool
 PortGroup::has_port (std::string const& p) const
 {
-	for (vector<boost::shared_ptr<ARDOUR::Bundle> >::const_iterator i = bundles.begin(); i != bundles.end(); ++i) {
+	for (ARDOUR::BundleList::const_iterator i = bundles.begin(); i != bundles.end(); ++i) {
 		if ((*i)->offers_port_alone (p)) {
 			return true;
 		}
@@ -111,40 +111,29 @@ PortGroupUI::setup_visibility_checkbutton ()
 }
 
 /** PortGroupList constructor.
- *  @param session Session to get bundles from.
  *  @param type Type of bundles to offer (audio or MIDI)
  *  @param offer_inputs true to offer output bundles, otherwise false.
- *  @param mask Mask of groups to make visible by default.
  */
 
-PortGroupList::PortGroupList (ARDOUR::Session & session, ARDOUR::DataType type, bool offer_inputs, Mask mask)
-	: _session (session), _type (type), _offer_inputs (offer_inputs),
-	  _buss (_("Bus"), mask & BUSS),
-	  _track (_("Track"), mask & TRACK),
-	  _system (_("System"), mask & SYSTEM),
-	  _other (_("Other"), mask & OTHER)
+PortGroupList::PortGroupList (ARDOUR::DataType type, bool offer_inputs)
+	: _type (type), _offer_inputs (offer_inputs),
+	  _buss (_("Bus"), true),
+	  _track (_("Track"), true),
+	  _system (_("System"), true),
+	  _other (_("Other"), true)
 {
-	refresh ();
-
-	for (iterator i = begin(); i != end(); ++i) {
-		(*i)->VisibilityChanged.connect (sigc::mem_fun (*this, &PortGroupList::visibility_changed));
-	}
+	
 }
 
-/** Find or re-find all our bundles and set up our lists */
+/** Gather bundles from around the system and put them in this PortGroupList */
 void
-PortGroupList::refresh ()
+PortGroupList::gather (ARDOUR::Session& session)
 {
-	clear ();
-
-	_buss.clear ();
-	_track.clear ();
-	_system.clear ();
-	_other.clear ();
+	clear_list ();
 
 	/* Find the bundles for routes */
 
-	boost::shared_ptr<ARDOUR::Session::RouteList> routes = _session.get_routes ();
+	boost::shared_ptr<ARDOUR::Session::RouteList> routes = session.get_routes ();
 
 	for (ARDOUR::Session::RouteList::const_iterator i = routes->begin(); i != routes->end(); ++i) {
 
@@ -174,20 +163,25 @@ PortGroupList::refresh ()
 	}
 
 	/* Bundles created by the session */
-	_session.foreach_bundle (sigc::mem_fun (*this, &PortGroupList::maybe_add_session_bundle));
+	boost::shared_ptr<ARDOUR::BundleList> b = session.bundles ();
+	for (ARDOUR::BundleList::iterator i = b->begin(); i != b->end(); ++i) {
+		if ((*i)->ports_are_inputs() == _offer_inputs && (*i)->type() == _type) {
+			_system.bundles.push_back (*i);
+		}
+	}
 	
 	/* XXX: inserts, sends, plugin inserts? */
 	
 	/* Now find all other ports that we haven't thought of yet */
 
- 	const char **ports = _session.engine().get_ports ("", _type.to_jack_type(), _offer_inputs ? 
+ 	const char **ports = session.engine().get_ports ("", _type.to_jack_type(), _offer_inputs ? 
  							  JackPortIsInput : JackPortIsOutput);
  	if (ports) {
 
 		int n = 0;
 		string client_matching_string;
 
-		client_matching_string = _session.engine().client_name();
+		client_matching_string = session.engine().client_name();
 		client_matching_string += ':';
 
 		while (ports[n]) {
@@ -215,6 +209,12 @@ PortGroupList::refresh ()
 	push_back (&_buss);
 	push_back (&_track);
 	push_back (&_other);
+
+	for (iterator i = begin(); i != end(); ++i) {
+		_visibility_connections.push_back (
+			(*i)->VisibilityChanged.connect (sigc::mem_fun (*this, &PortGroupList::visibility_changed))
+			);
+	}
 }
 
 bool
@@ -236,20 +236,12 @@ PortGroupList::set_offer_inputs (bool i)
 	_offer_inputs = i;
 }
 
-void
-PortGroupList::maybe_add_session_bundle (boost::shared_ptr<ARDOUR::Bundle> b)
+ARDOUR::BundleList
+PortGroupList::bundles () const
 {
-	if (b->ports_are_inputs () == _offer_inputs && b->type () == _type) {
-		_system.bundles.push_back (b);
-	}
-}
-
-std::vector<boost::shared_ptr<ARDOUR::Bundle> >
-PortGroupList::bundles ()
-{
-	std::vector<boost::shared_ptr<ARDOUR::Bundle> > bundles;
+	ARDOUR::BundleList bundles;
 		
-	for (iterator i = begin (); i != end (); ++i) {
+	for (const_iterator i = begin (); i != end (); ++i) {
 		if ((*i)->visible()) {
 			
 			std::copy ((*i)->bundles.begin(), (*i)->bundles.end(), std::back_inserter (bundles));
@@ -334,3 +326,20 @@ PortGroupList::take_visibility_from (PortGroupList const & o)
 		++j;
 	}
 }
+
+void
+PortGroupList::clear_list ()
+{
+	clear ();
+
+	_buss.clear ();
+	_track.clear ();
+	_system.clear ();
+	_other.clear ();
+
+	for (std::vector<sigc::connection>::iterator i = _visibility_connections.begin(); i != _visibility_connections.end(); ++i) {
+		i->disconnect ();
+	}
+
+	_visibility_connections.clear ();
+}
diff --git a/gtk2_ardour/port_group.h b/gtk2_ardour/port_group.h
index a5b5b109c4..17e9842f93 100644
--- a/gtk2_ardour/port_group.h
+++ b/gtk2_ardour/port_group.h
@@ -26,6 +26,7 @@
 #include <gtkmm/checkbutton.h>
 #include <boost/shared_ptr.hpp>
 #include <ardour/data_type.h>
+#include <ardour/types.h>
 
 namespace ARDOUR {
 	class Session;
@@ -53,7 +54,7 @@ public:
 	void clear ();
 
 	std::string name; ///< name for the group
-	std::vector<boost::shared_ptr<ARDOUR::Bundle> > bundles;
+	ARDOUR::BundleList bundles;
 	std::vector<std::string> ports;
 	bool visible () const {
 		return _visible;
@@ -95,30 +96,22 @@ class PortGroupUI
 class PortGroupList : public std::list<PortGroup*>, public sigc::trackable
 {
   public:
-	enum Mask {
-		BUSS = 0x1,
-		TRACK = 0x2,
-		SYSTEM = 0x4,
-		OTHER = 0x8
-	};
+	PortGroupList (ARDOUR::DataType, bool);
 
-	PortGroupList (ARDOUR::Session &, ARDOUR::DataType, bool, Mask);
-
-	void refresh ();
+	void gather (ARDOUR::Session &);
 	void set_type (ARDOUR::DataType);
 	void set_offer_inputs (bool);
-	std::vector<boost::shared_ptr<ARDOUR::Bundle> > bundles ();
+	ARDOUR::BundleList bundles () const;
 	void take_visibility_from (PortGroupList const &);
+	void clear_list ();
 
 	sigc::signal<void> VisibilityChanged;
 	
   private:
-	void maybe_add_session_bundle (boost::shared_ptr<ARDOUR::Bundle>);
 	bool port_has_prefix (std::string const &, std::string const &) const;
 	std::string common_prefix (std::vector<std::string> const &) const;
 	void visibility_changed ();
 	
-	ARDOUR::Session& _session;
 	ARDOUR::DataType _type;
 	bool _offer_inputs;
 
@@ -126,6 +119,8 @@ class PortGroupList : public std::list<PortGroup*>, public sigc::trackable
 	PortGroup _track;
 	PortGroup _system;
 	PortGroup _other;
+
+	std::vector<sigc::connection> _visibility_connections;
 };
 
 #endif /* __gtk_ardour_port_group_h__ */
diff --git a/gtk2_ardour/port_matrix.cc b/gtk2_ardour/port_matrix.cc
index 5d6ea37408..fccc707694 100644
--- a/gtk2_ardour/port_matrix.cc
+++ b/gtk2_ardour/port_matrix.cc
@@ -22,6 +22,7 @@
 #include <gtkmm/adjustment.h>
 #include <gtkmm/label.h>
 #include "ardour/bundle.h"
+#include "ardour/types.h"
 #include "port_matrix.h"
 #include "i18n.h"
 
@@ -29,20 +30,23 @@
  *  @param session Our session.
  *  @param type Port type that we are handling.
  *  @param offer_inputs true to offer inputs, otherwise false.
- *  @param mask Mask of port groups to offer.
  */
-PortMatrix::PortMatrix (ARDOUR::Session& session, ARDOUR::DataType type, bool offer_inputs, PortGroupList::Mask mask)
-	: _port_group_list (session, type, offer_inputs, mask),
+PortMatrix::PortMatrix (ARDOUR::Session& session, ARDOUR::DataType type, bool offer_inputs)
+	: _row_ports (type, !offer_inputs),
+	  _column_ports (type, offer_inputs),
+	  _session (session),
 	  _offer_inputs (offer_inputs),
 	  _type (type),
 	  _body (this, offer_inputs ? PortMatrixBody::BOTTOM_AND_LEFT : PortMatrixBody::TOP_AND_RIGHT)
 {
+	setup ();
+	
 	/* checkbuttons for visibility of groups */
 	Gtk::HBox* visibility_buttons = Gtk::manage (new Gtk::HBox);
 
 	visibility_buttons->pack_start (*Gtk::manage (new Gtk::Label (_("Show:"))), Gtk::PACK_SHRINK);
-	
-	for (std::list<PortGroup*>::iterator i = _port_group_list.begin(); i != _port_group_list.end(); ++i) {
+
+	for (std::list<PortGroup*>::iterator i = _column_ports.begin(); i != _column_ports.end(); ++i) {
 		_port_group_uis.push_back (new PortGroupUI (this, *i));
 	}
 
@@ -76,8 +80,8 @@ PortMatrix::~PortMatrix ()
 void
 PortMatrix::setup ()
 {
-	_port_group_list.refresh ();
-	_body.setup (_our_bundles, _port_group_list.bundles ());
+	_column_ports.gather (_session);
+	_body.setup (_row_ports, _column_ports);
 	setup_scrollbars ();
 	queue_draw ();
 }
@@ -86,7 +90,8 @@ void
 PortMatrix::set_offer_inputs (bool s)
 {
 	_offer_inputs = s;
-	_port_group_list.set_offer_inputs (s);
+	_column_ports.set_offer_inputs (s);
+	_row_ports.set_offer_inputs (!s);
 	setup ();
 }
 
@@ -94,7 +99,8 @@ void
 PortMatrix::set_type (ARDOUR::DataType t)
 {
 	_type = t;
-	_port_group_list.set_type (t);
+	_column_ports.set_type (t);
+	_row_ports.set_type (t);
 	setup ();
 }
 
@@ -131,18 +137,17 @@ PortMatrix::setup_scrollbars ()
 void
 PortMatrix::disassociate_all ()
 {
-	for (PortGroupList::iterator i = _port_group_list.begin(); i != _port_group_list.end(); ++i) {
-		
-		for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::iterator j = (*i)->bundles.begin(); j != (*i)->bundles.end(); ++j) {
+	ARDOUR::BundleList c = _column_ports.bundles ();
+	ARDOUR::BundleList r = _row_ports.bundles ();
+	
+	for (ARDOUR::BundleList::iterator i = c.begin(); i != c.end(); ++i) {
+		for (uint32_t j = 0; j < (*i)->nchannels(); ++j) {
+			for (uint32_t k = 0; k < r.front()->nchannels(); ++k) {
 
-			for (uint32_t k = 0; k < (*j)->nchannels(); ++k) {
-
-				for (uint32_t l = 0; l < _our_bundles.front()->nchannels(); ++l) {
-
-					set_state (
-						_our_bundles.front(), l, *j, k, false, 0
-						);
-				}
+				set_state (
+					r.front(), k, *i, j, false, 0
+					);
+				
 			}
 		}
 	}
diff --git a/gtk2_ardour/port_matrix.h b/gtk2_ardour/port_matrix.h
index ad6730976d..85a273265e 100644
--- a/gtk2_ardour/port_matrix.h
+++ b/gtk2_ardour/port_matrix.h
@@ -46,13 +46,21 @@ namespace ARDOUR {
 class PortMatrix : public Gtk::VBox
 {
 public:
-	PortMatrix (ARDOUR::Session&, ARDOUR::DataType, bool, PortGroupList::Mask);
+	PortMatrix (ARDOUR::Session&, ARDOUR::DataType, bool);
 	~PortMatrix ();
 
 	virtual void setup ();
 	void set_offer_inputs (bool);
 	void set_type (ARDOUR::DataType);
-	bool offering_input () const { return _offer_inputs; }
+
+	ARDOUR::DataType type () const {
+		return _type;
+	}
+	
+	bool offering_input () const {
+		return _offer_inputs;
+	}
+	
 	void disassociate_all ();
 
 	enum Result {
@@ -106,15 +114,15 @@ public:
 
 protected:
 
-	std::vector<boost::shared_ptr<ARDOUR::Bundle> > _our_bundles;
-	/// list of port groups
-	PortGroupList _port_group_list;
+	PortGroupList _row_ports;
+	PortGroupList _column_ports;
 	
 private:
 
 	void hscroll_changed ();
 	void vscroll_changed ();
-	
+
+	ARDOUR::Session& _session;
 	/// true to offer inputs, otherwise false
 	bool _offer_inputs;
 	/// port type that we are working with
diff --git a/gtk2_ardour/port_matrix_body.cc b/gtk2_ardour/port_matrix_body.cc
index d9d8013578..3531712a56 100644
--- a/gtk2_ardour/port_matrix_body.cc
+++ b/gtk2_ardour/port_matrix_body.cc
@@ -19,6 +19,7 @@
 
 #include <iostream>
 #include "ardour/bundle.h"
+#include "ardour/types.h"
 #include "port_matrix_body.h"
 #include "port_matrix.h"
 
@@ -29,7 +30,9 @@ PortMatrixBody::PortMatrixBody (PortMatrix* p, Arrangement a)
 	  _grid (p, this),
 	  _arrangement (a),
 	  _xoffset (0),
-	  _yoffset (0)
+	  _yoffset (0),
+	  _column_ports (_port_matrix->type(), _port_matrix->offering_input()),
+	  _row_ports (_port_matrix->type(), !_port_matrix->offering_input())
 {
 	modify_bg (Gtk::STATE_NORMAL, Gdk::Color ("#00000"));
 }
@@ -215,10 +218,7 @@ PortMatrixBody::compute_rectangles ()
 }
 
 void
-PortMatrixBody::setup (
-	std::vector<boost::shared_ptr<ARDOUR::Bundle> > const & row,
-	std::vector<boost::shared_ptr<ARDOUR::Bundle> > const & column
-	)
+PortMatrixBody::setup (PortGroupList const& row, PortGroupList const& column)
 {
 	for (std::list<sigc::connection>::iterator i = _bundle_connections.begin(); i != _bundle_connections.end(); ++i) {
 		i->disconnect ();
@@ -226,10 +226,11 @@ PortMatrixBody::setup (
 
 	_bundle_connections.clear ();
 	
-	_row_bundles = row;
-	_column_bundles = column;
+	_row_ports = row;
+	_column_ports = column;
 
-	for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::iterator i = _row_bundles.begin(); i != _row_bundles.end(); ++i) {
+	ARDOUR::BundleList r = _row_ports.bundles ();
+	for (ARDOUR::BundleList::iterator i = r.begin(); i != r.end(); ++i) {
 		
 		_bundle_connections.push_back (
 			(*i)->NameChanged.connect (sigc::mem_fun (*this, &PortMatrixBody::rebuild_and_draw_row_labels))
@@ -237,7 +238,8 @@ PortMatrixBody::setup (
 		
 	}
 
-	for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::iterator i = _column_bundles.begin(); i != _column_bundles.end(); ++i) {
+	ARDOUR::BundleList c = _column_ports.bundles ();
+	for (ARDOUR::BundleList::iterator i = c.begin(); i != c.end(); ++i) {
 		_bundle_connections.push_back (
 			(*i)->NameChanged.connect (sigc::mem_fun (*this, &PortMatrixBody::rebuild_and_draw_column_labels))
 			);
diff --git a/gtk2_ardour/port_matrix_body.h b/gtk2_ardour/port_matrix_body.h
index 753f4f7096..c9fd8bdb65 100644
--- a/gtk2_ardour/port_matrix_body.h
+++ b/gtk2_ardour/port_matrix_body.h
@@ -23,6 +23,7 @@
 #include "port_matrix_column_labels.h"
 #include "port_matrix_row_labels.h"
 #include "port_matrix_grid.h"
+#include "port_group.h"
 
 class PortMatrix;
 
@@ -40,20 +41,17 @@ public:
 
 	PortMatrixBody (PortMatrix *, Arrangement);
 
-	/** @return bundles to offer for columns */
-	std::vector<boost::shared_ptr<ARDOUR::Bundle> > const & column_bundles () {
-		return _column_bundles;
+	/** @return ports to offer for columns */
+	PortGroupList const & column_ports () {
+		return _column_ports;
 	}
 
-	/** @return bundles to offer for rows */
-	std::vector<boost::shared_ptr<ARDOUR::Bundle> > const & row_bundles () {
-		return _row_bundles;
+	/** @return ports to offer for rows */
+	PortGroupList const & row_ports () {
+		return _row_ports;
 	}
 	
-	void setup (
-		std::vector<boost::shared_ptr<ARDOUR::Bundle> > const &,
-		std::vector<boost::shared_ptr<ARDOUR::Bundle> > const &
-		);
+	void setup (PortGroupList const &, PortGroupList const &);
 
 	uint32_t full_scroll_width ();
 	uint32_t alloc_scroll_width ();
@@ -91,9 +89,9 @@ private:
 	uint32_t _yoffset;
 
 	/// bundles to offer for columns
-	std::vector<boost::shared_ptr<ARDOUR::Bundle> > _column_bundles;
+	PortGroupList _column_ports;
 	/// bundles to offer for rows
-	std::vector<boost::shared_ptr<ARDOUR::Bundle> > _row_bundles;
+	PortGroupList _row_ports;
 
 	std::list<sigc::connection> _bundle_connections;
 };
diff --git a/gtk2_ardour/port_matrix_column_labels.cc b/gtk2_ardour/port_matrix_column_labels.cc
index 72954d1627..3ef501d89b 100644
--- a/gtk2_ardour/port_matrix_column_labels.cc
+++ b/gtk2_ardour/port_matrix_column_labels.cc
@@ -19,6 +19,7 @@
 
 #include <iostream>
 #include "ardour/bundle.h"
+#include "ardour/types.h"
 #include "port_matrix_column_labels.h"
 #include "port_matrix.h"
 
@@ -39,10 +40,13 @@ PortMatrixColumnLabels::compute_dimensions ()
 	_longest_bundle_name = 0;
 	/* width of the longest channel name */
 	_longest_channel_name = 0;
-	/* height of highest bit of text */
+	/* height of highest bit of text (apart from group names) */
 	_highest_text = 0;
-	
-	for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::const_iterator i = _body->column_bundles().begin (); i != _body->column_bundles().end(); ++i) {
+	/* width of the whole thing */
+	_width = 0;
+
+	ARDOUR::BundleList const c = _body->column_ports().bundles();
+	for (ARDOUR::BundleList::const_iterator i = c.begin (); i != c.end(); ++i) {
 
 		cairo_text_extents_t ext;
 		cairo_text_extents (cr, (*i)->name().c_str(), &ext);
@@ -68,23 +72,33 @@ PortMatrixColumnLabels::compute_dimensions ()
 				_highest_text = ext.height;
 			}
 		}
+
+		_width += (*i)->nchannels() * column_width();
+	}
+
+	_highest_group_name = 0;
+	for (PortGroupList::const_iterator i = _body->column_ports().begin(); i != _body->column_ports().end(); ++i) {
+		if ((*i)->visible()) {
+			cairo_text_extents_t ext;
+			cairo_text_extents (cr, (*i)->name.c_str(), &ext);
+			if (ext.height > _highest_group_name) {
+				_highest_group_name = ext.height;
+			}
+		}
 	}
 
 	cairo_destroy (cr);
 	gdk_pixmap_unref (pm);
 
-	/* width and height of the whole thing */
-	
-	_width = 0;
-	for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::const_iterator i = _body->column_bundles().begin (); i != _body->column_bundles().end(); ++i) {
-		_width += (*i)->nchannels() * column_width();
-	}
+	/* height of the whole thing */
 
-	_height =
+	double const parallelogram_height = 
 		(_longest_bundle_name + _longest_channel_name + 4 * name_pad()) * sin (angle())
 		+ _highest_text * cos (angle());
 
-	_width += _height / tan (angle ());
+	_height = parallelogram_height + _highest_group_name + 2 * name_pad();
+
+	_width += parallelogram_height / tan (angle ());
 }
 
 double
@@ -103,28 +117,84 @@ PortMatrixColumnLabels::render (cairo_t* cr)
 	cairo_rectangle (cr, 0, 0, _width, _height);
 	cairo_fill (cr);
 
+	/* PORT GROUP NAME */
+	
+	double x = 0;
+	double y = 0;
+	
+	if (_location == TOP) {
+		x = (_height - _highest_group_name - 2 * name_pad()) / tan (angle());
+		y = _highest_group_name + name_pad();
+	} else {
+		x = 0;
+		y = _height - name_pad();
+	}
+
+	int g = 0;
+	for (PortGroupList::const_iterator i = _body->column_ports().begin(); i != _body->column_ports().end(); ++i) {
+
+		if (!(*i)->visible() || ((*i)->bundles.empty() && (*i)->ports.empty()) ) {
+			continue;
+		}
+
+		/* compute width of this group */
+		uint32_t w = 0;
+		for (ARDOUR::BundleList::const_iterator j = (*i)->bundles.begin(); j != (*i)->bundles.end(); ++j) {
+			w += (*j)->nchannels() * column_width();
+		}
+		w += (*i)->ports.size() * column_width();
+
+		/* rectangle */
+		set_source_rgb (cr, get_a_group_colour (g));
+		double const rh = _highest_group_name + 2 * name_pad();
+		if (_location == TOP) {
+			cairo_rectangle (cr, x, 0, w, rh);
+		} else if (_location == BOTTOM) {
+			cairo_rectangle (cr, x, _height - rh, w, rh);
+		}
+		cairo_fill (cr);
+		
+		std::pair<std::string, double> const display = display_port_name (cr, (*i)->name, w);
+
+		/* plot it */
+		set_source_rgb (cr, text_colour());
+		cairo_move_to (cr, x + (w - display.second) / 2, y);
+		cairo_show_text (cr, display.first.c_str());
+
+		x += w;
+		++g;
+	}
+
         /* BUNDLE PARALLELOGRAM-TYPE-THING AND NAME */
 
-	double x = 0;
-	for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::const_iterator i = _body->column_bundles().begin (); i != _body->column_bundles().end(); ++i) {
+	x = 0;
+	ARDOUR::BundleList const c = _body->column_ports().bundles();
+	for (ARDOUR::BundleList::const_iterator i = c.begin (); i != c.end(); ++i) {
 
-		Gdk::Color colour = get_a_bundle_colour (i - _body->column_bundles().begin ());
+		Gdk::Color colour = get_a_bundle_colour (i - c.begin ());
 		set_source_rgb (cr, colour);
 
 		double const w = (*i)->nchannels() * column_width();
+		double const ph = _height - _highest_group_name - 2 * name_pad();
 
 		double x_ = x;
-		double y_ = _height;
 		
-		cairo_move_to (cr, x_, y_);
-		x_ += w;
-		cairo_line_to (cr, x_, y_);
-		x_ += _height / tan (angle ());
-		y_ -= _height;
-		cairo_line_to (cr, x_, y_);
-		x_ -= w;
-		cairo_line_to (cr, x_, y_);
-		cairo_line_to (cr, x, _height);
+		if (_location == TOP) {
+			y = _height;
+		} else if (_location == BOTTOM) {
+			y = ph;
+		}
+
+		double y_ = y;
+ 		cairo_move_to (cr, x_, y_);
+ 		x_ += w;
+ 		cairo_line_to (cr, x_, y_);
+ 		x_ += ph / tan (angle ());
+ 		y_ -= ph;
+ 		cairo_line_to (cr, x_, y_);
+ 		x_ -= w;
+ 		cairo_line_to (cr, x_, y_);
+ 		cairo_line_to (cr, x, y);
 		cairo_fill_preserve (cr);
 		set_source_rgb (cr, background_colour());
 		cairo_set_line_width (cr, label_border_width());
@@ -132,7 +202,6 @@ PortMatrixColumnLabels::render (cairo_t* cr)
 
 		set_source_rgb (cr, text_colour());
 
-
 		if (_location == TOP) {
 			
 			double const rl = 3 * name_pad() + _longest_channel_name;
@@ -147,7 +216,7 @@ PortMatrixColumnLabels::render (cairo_t* cr)
 			cairo_move_to (
 				cr,
 				x + basic_text_x_pos (0),
-				_height - name_pad() * sin (angle())
+				ph - name_pad() * sin (angle())
 				);
 		}
 			
@@ -163,16 +232,17 @@ PortMatrixColumnLabels::render (cairo_t* cr)
 	/* PORT NAMES */
 
 	x = 0;
-	for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::const_iterator i = _body->column_bundles().begin(); i != _body->column_bundles().end(); ++i) {
+	for (ARDOUR::BundleList::const_iterator i = c.begin (); i != c.end(); ++i) {
 		
 		for (uint32_t j = 0; j < (*i)->nchannels(); ++j) {
 
 			double const lc = _longest_channel_name + name_pad();
 			double const w = column_width();
+			double const ph = _height - _highest_group_name - 2 * name_pad();
 
 			if (_location == BOTTOM) {
 
-				double x_ = x + _height / tan (angle()) + w;
+				double x_ = x + ph / tan (angle()) + w;
 				double const ix = x_;
 				double y_ = 0;
 				cairo_move_to (cr, x_, y_);
@@ -203,7 +273,7 @@ PortMatrixColumnLabels::render (cairo_t* cr)
 
 			}
 
-			Gdk::Color colour = get_a_bundle_colour (i - _body->column_bundles().begin());
+			Gdk::Color colour = get_a_bundle_colour (i - c.begin());
 			set_source_rgb (cr, colour);
 			cairo_fill_preserve (cr);
 			set_source_rgb (cr, background_colour());
@@ -216,7 +286,7 @@ PortMatrixColumnLabels::render (cairo_t* cr)
 				cairo_move_to (cr, x + basic_text_x_pos(j), _height - name_pad() * sin (angle()));
 			} else if (_location == BOTTOM) {
 				double const rl = 3 * name_pad() + _longest_bundle_name;
-				cairo_move_to (cr, x + basic_text_x_pos(j) + rl * cos (angle ()), _height - rl * sin (angle()));
+				cairo_move_to (cr, x + basic_text_x_pos(j) + rl * cos (angle ()), ph - rl * sin (angle()));
 			}
 			
 			cairo_save (cr);
diff --git a/gtk2_ardour/port_matrix_column_labels.h b/gtk2_ardour/port_matrix_column_labels.h
index 76510073ec..5bdd7a2930 100644
--- a/gtk2_ardour/port_matrix_column_labels.h
+++ b/gtk2_ardour/port_matrix_column_labels.h
@@ -50,6 +50,7 @@ private:
 	double _longest_bundle_name;
 	double _longest_channel_name;
 	double _highest_text;
+	double _highest_group_name;
 	Location _location;
 };
 
diff --git a/gtk2_ardour/port_matrix_component.cc b/gtk2_ardour/port_matrix_component.cc
index e2d1e07027..74f989934e 100644
--- a/gtk2_ardour/port_matrix_component.cc
+++ b/gtk2_ardour/port_matrix_component.cc
@@ -105,3 +105,35 @@ PortMatrixComponent::dimensions ()
 
 	return std::make_pair (_width, _height);
 }
+
+std::pair<std::string, double>
+PortMatrixComponent::display_port_name (cairo_t* cr, std::string const &n, double avail) const
+{
+	/* XXX hopefully there exists a more efficient way of doing this */
+	
+	Glib::ustring name = Glib::ustring (n).uppercase ();
+	bool abbreviated = false;
+	uint32_t width = 0;
+		
+	while (1) {
+		if (name.length() <= 2) {
+			break;
+		}
+			
+		cairo_text_extents_t ext;
+		cairo_text_extents (cr, name.c_str(), &ext);
+		if (ext.width < avail) {
+			width = ext.width;
+			break;
+		}
+			
+		if (abbreviated) {
+			name = name.substr (0, name.length() - 2) + ".";
+		} else {
+			name = name.substr (0, name.length() - 1) + ".";
+			abbreviated = true;
+		}
+	}
+
+	return std::make_pair (name, width);
+}
diff --git a/gtk2_ardour/port_matrix_component.h b/gtk2_ardour/port_matrix_component.h
index 7c836ee96f..cc0f082695 100644
--- a/gtk2_ardour/port_matrix_component.h
+++ b/gtk2_ardour/port_matrix_component.h
@@ -124,8 +124,18 @@ protected:
 		}
 	}
 
+	/* XXX */
+	static Gdk::Color get_a_group_colour (int x) {
+		if ((x % 2) == 0) {
+			return Gdk::Color ("#222222");
+		} else {
+			return Gdk::Color ("#444444");
+		}
+	}
+	
 	void set_source_rgb (cairo_t *, Gdk::Color const &);
 	void set_source_rgba (cairo_t *, Gdk::Color const &, double);
+	std::pair<std::string, double> display_port_name (cairo_t*, std::string const &, double) const;
 
 	/** Render the complete component to a cairo context. */
 	virtual void render (cairo_t *) = 0;
diff --git a/gtk2_ardour/port_matrix_grid.cc b/gtk2_ardour/port_matrix_grid.cc
index f63cd231d7..bab229efaf 100644
--- a/gtk2_ardour/port_matrix_grid.cc
+++ b/gtk2_ardour/port_matrix_grid.cc
@@ -20,6 +20,7 @@
 #include <iostream>
 #include <cairo/cairo.h>
 #include "ardour/bundle.h"
+#include "ardour/types.h"
 #include "port_matrix_grid.h"
 #include "port_matrix.h"
 
@@ -34,13 +35,15 @@ void
 PortMatrixGrid::compute_dimensions ()
 {
 	_width = 0;
-	for (uint32_t i = 0; i < _body->column_bundles().size(); ++i) {
-		_width += _body->column_bundles()[i]->nchannels() * column_width();
+	ARDOUR::BundleList const c = _body->column_ports().bundles();
+	for (ARDOUR::BundleList::const_iterator i = c.begin(); i != c.end(); ++i) {
+		_width += (*i)->nchannels() * column_width();
 	}
 
 	_height = 0;
-	for (uint32_t i = 0; i < _body->row_bundles().size(); ++i) {
-		_height += _body->row_bundles()[i]->nchannels() * row_height();
+	ARDOUR::BundleList const r = _body->row_ports().bundles();
+	for (ARDOUR::BundleList::const_iterator i = r.begin(); i != r.end(); ++i) {
+		_height += (*i)->nchannels() * row_height();
 	}
 }
 
@@ -58,17 +61,18 @@ PortMatrixGrid::render (cairo_t* cr)
 	
 	set_source_rgb (cr, grid_colour());
 	uint32_t x = 0;
-	for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::size_type i = 0; i < _body->column_bundles().size(); ++i) {
+	ARDOUR::BundleList const c = _body->column_ports().bundles();
+	for (ARDOUR::BundleList::size_type i = 0; i < c.size(); ++i) {
 
 		cairo_set_line_width (cr, thin_grid_line_width());
-		for (uint32_t j = 1; j < _body->column_bundles()[i]->nchannels(); ++j) {
+		for (uint32_t j = 1; j < c[i]->nchannels(); ++j) {
 			x += column_width();
 			cairo_move_to (cr, x, 0);
 			cairo_line_to (cr, x, _height);
 			cairo_stroke (cr);
 		}
 
-		if (i < (_body->column_bundles().size() - 1)) {
+		if (i < (c.size() - 1)) {
 			x += column_width();
 			cairo_set_line_width (cr, thick_grid_line_width());
 			cairo_move_to (cr, x, 0);
@@ -82,17 +86,18 @@ PortMatrixGrid::render (cairo_t* cr)
 	/* HORIZONTAL GRID LINES */
 	
 	uint32_t y = 0;
-	for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::size_type i = 0; i < _body->row_bundles().size(); ++i) {
+	ARDOUR::BundleList const r = _body->row_ports().bundles();
+	for (ARDOUR::BundleList::size_type i = 0; i < r.size(); ++i) {
 
 		cairo_set_line_width (cr, thin_grid_line_width());
-		for (uint32_t j = 1; j < _body->row_bundles()[i]->nchannels(); ++j) {
+		for (uint32_t j = 1; j < r[i]->nchannels(); ++j) {
 			y += row_height();
 			cairo_move_to (cr, 0, y);
 			cairo_line_to (cr, grid_width, y);
 			cairo_stroke (cr);
 		}
 
-		if (i < (_body->row_bundles().size() - 1)) {
+		if (i < (r.size() - 1)) {
 			y += row_height();
 			cairo_set_line_width (cr, thick_grid_line_width());
 			cairo_move_to (cr, 0, y);
@@ -106,10 +111,10 @@ PortMatrixGrid::render (cairo_t* cr)
 	uint32_t bx = 0;
 	uint32_t by = 0;
 	
-	for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::const_iterator i = _body->column_bundles().begin(); i < _body->column_bundles().end(); ++i) {
+	for (ARDOUR::BundleList::const_iterator i = c.begin(); i < c.end(); ++i) {
 		by = 0;
 		
-		for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::const_iterator j = _body->row_bundles().begin(); j < _body->row_bundles().end(); ++j) {
+		for (ARDOUR::BundleList::const_iterator j = r.begin(); j < r.end(); ++j) {
 
 			x = bx;
 			for (uint32_t k = 0; k < (*i)->nchannels (); k++) {
@@ -174,7 +179,8 @@ PortMatrixGrid::button_press (double x, double y, int b)
 	boost::shared_ptr<ARDOUR::Bundle> other_bundle;
 	uint32_t other_channel = 0;
 
-	for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::const_iterator i = _body->row_bundles().begin(); i != _body->row_bundles().end(); ++i) {
+	ARDOUR::BundleList const r = _body->row_ports().bundles();
+	for (ARDOUR::BundleList::const_iterator i = r.begin(); i != r.end(); ++i) {
 		if (grid_row < (*i)->nchannels ()) {
 			our_bundle = *i;
 			our_channel = grid_row;
@@ -184,7 +190,8 @@ PortMatrixGrid::button_press (double x, double y, int b)
 		}
 	}
 
-	for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::const_iterator i = _body->column_bundles().begin(); i != _body->column_bundles().end(); ++i) {
+	ARDOUR::BundleList const c = _body->column_ports().bundles();
+	for (ARDOUR::BundleList::const_iterator i = c.begin(); i != c.end(); ++i) {
 		if (grid_column < (*i)->nchannels ()) {
 			other_bundle = *i;
 			other_channel = grid_column;
diff --git a/gtk2_ardour/port_matrix_grid.h b/gtk2_ardour/port_matrix_grid.h
index 298d33c0b5..7441d3c79d 100644
--- a/gtk2_ardour/port_matrix_grid.h
+++ b/gtk2_ardour/port_matrix_grid.h
@@ -44,9 +44,6 @@ private:
 	void compute_dimensions ();
 	void render (cairo_t *);
 
-	std::vector<boost::shared_ptr<ARDOUR::Bundle> > _column_bundles;
-	std::vector<boost::shared_ptr<ARDOUR::Bundle> > _row_bundles;
-
 	PortMatrix* _port_matrix;
 };
 
diff --git a/gtk2_ardour/port_matrix_row_labels.cc b/gtk2_ardour/port_matrix_row_labels.cc
index ab9480ac65..7740d9cf18 100644
--- a/gtk2_ardour/port_matrix_row_labels.cc
+++ b/gtk2_ardour/port_matrix_row_labels.cc
@@ -47,7 +47,10 @@ PortMatrixRowLabels::compute_dimensions ()
 	cairo_t* cr = gdk_cairo_create (pm);
 	
 	_longest_port_name = 0;
-	for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::const_iterator i = _body->row_bundles().begin(); i != _body->row_bundles().end(); ++i) {
+	_longest_bundle_name = 0;
+	_height = 0;
+	ARDOUR::BundleList const r = _body->row_ports().bundles();
+	for (ARDOUR::BundleList::const_iterator i = r.begin(); i != r.end(); ++i) {
 		for (uint32_t j = 0; j < (*i)->nchannels(); ++j) {
 			cairo_text_extents_t ext;
 			cairo_text_extents (cr, (*i)->channel_name(j).c_str(), &ext);
@@ -55,26 +58,34 @@ PortMatrixRowLabels::compute_dimensions ()
 				_longest_port_name = ext.width;
 			}
 		}
-	}
 
-	_longest_bundle_name = 0;
-	for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::const_iterator i = _body->row_bundles().begin(); i != _body->row_bundles().end(); ++i) {
 		cairo_text_extents_t ext;
 		cairo_text_extents (cr, (*i)->name().c_str(), &ext);
 		if (ext.width > _longest_bundle_name) {
 			_longest_bundle_name = ext.width;
 		}
-	}
 
-	cairo_destroy (cr);
-	gdk_pixmap_unref (pm);
-
-	_height = 0;
-	for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::const_iterator i = _body->row_bundles().begin(); i != _body->row_bundles().end(); ++i) {
 		_height += (*i)->nchannels() * row_height();
 	}
 
-	_width = _longest_port_name + name_pad() * 4 + _longest_bundle_name;
+	_highest_group_name = 0;
+	for (PortGroupList::const_iterator i = _body->row_ports().begin(); i != _body->row_ports().end(); ++i) {
+		if ((*i)->visible()) {
+			cairo_text_extents_t ext;
+			cairo_text_extents (cr, (*i)->name.c_str(), &ext);
+			if (ext.height > _highest_group_name) {
+				_highest_group_name = ext.height;
+			}
+		}
+	}
+			
+	cairo_destroy (cr);
+	gdk_pixmap_unref (pm);
+
+	_width = _highest_group_name +
+		_longest_port_name +
+		_longest_bundle_name +
+		name_pad() * 6;
 }
 
 
@@ -87,27 +98,73 @@ PortMatrixRowLabels::render (cairo_t* cr)
 	cairo_rectangle (cr, 0, 0, _width, _height);
 	cairo_fill (cr);
 
-	/* SIDE BUNDLE NAMES */
+	/* PORT GROUP NAMES */
 
-	uint32_t x = 0;
+	double x = 0;
 	if (_location == LEFT) {
-		x = name_pad();
+		x = 0;
 	} else if (_location == RIGHT) {
-		x = _longest_port_name + name_pad() * 3;
+		x = _width - _highest_group_name - 2 * name_pad();
 	}
 
-	uint32_t y = 0;
-	for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::const_iterator i = _body->row_bundles().begin(); i != _body->row_bundles().end(); ++i) {
+	double y = 0;
+	int g = 0;
+	for (PortGroupList::const_iterator i = _body->row_ports().begin(); i != _body->row_ports().end(); ++i) {
 
-		Gdk::Color const colour = get_a_bundle_colour (i - _body->row_bundles().begin ());
+		if (!(*i)->visible() || ((*i)->bundles.empty() && (*i)->ports.empty()) ) {
+			continue;
+		}
+			
+		/* compute height of this group */
+		double h = 0;
+		for (ARDOUR::BundleList::const_iterator j = (*i)->bundles.begin(); j != (*i)->bundles.end(); ++j) {
+			h += (*j)->nchannels() * row_height();
+		}
+		h += (*i)->ports.size() * row_height();
+
+		/* rectangle */
+		set_source_rgb (cr, get_a_group_colour (g));
+		double const rw = _highest_group_name + 2 * name_pad();
+		cairo_rectangle (cr, x, y, rw, h);
+		cairo_fill (cr);
+		    
+		/* hence what abbreviation (or not) we need for the group name */
+		std::pair<std::string, double> display = display_port_name (cr, (*i)->name, h);
+
+		/* plot it */
+		set_source_rgb (cr, text_colour());
+		cairo_move_to (cr, x + rw - name_pad(), y + (h + display.second) / 2);
+		cairo_save (cr);
+		cairo_rotate (cr, - M_PI / 2);
+		cairo_show_text (cr, display.first.c_str());
+		cairo_restore (cr);
+
+		y += h;
+		++g;
+	}
+
+	/* SIDE BUNDLE NAMES */
+
+	x = 0;
+	if (_location == LEFT) {
+		x = _highest_group_name + 2 * name_pad();
+	} else if (_location == RIGHT) {
+		x = _longest_port_name + name_pad() * 2;
+	}
+
+	y = 0;
+	ARDOUR::BundleList const r = _body->row_ports().bundles();
+	for (ARDOUR::BundleList::const_iterator i = r.begin(); i != r.end(); ++i) {
+
+		Gdk::Color const colour = get_a_bundle_colour (i - r.begin ());
 		set_source_rgb (cr, colour);
-		cairo_rectangle (cr, 0, y, _width, row_height() * (*i)->nchannels());
+		cairo_rectangle (cr, x, y, _longest_bundle_name + name_pad() * 2, row_height() * (*i)->nchannels());
 		cairo_fill_preserve (cr);
 		set_source_rgb (cr, background_colour());
 		cairo_set_line_width (cr, label_border_width ());
 		cairo_stroke (cr);
 
-		uint32_t off = 0;
+		double off = 0;
 		if ((*i)->nchannels () > 0) {
 			/* use the extent of our first channel name so that the bundle name is vertically aligned with it */
 			cairo_text_extents_t ext;
@@ -118,7 +175,7 @@ PortMatrixRowLabels::render (cairo_t* cr)
 		}
 
 		set_source_rgb (cr, text_colour());
-		cairo_move_to (cr, x, y + name_pad() + off);
+		cairo_move_to (cr, x + name_pad(), y + name_pad() + off);
 		cairo_show_text (cr, (*i)->name().c_str());
 		
 		y += row_height() * (*i)->nchannels ();
@@ -128,17 +185,17 @@ PortMatrixRowLabels::render (cairo_t* cr)
 	/* SIDE PORT NAMES */
 
 	y = 0;
-	for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::const_iterator i = _body->row_bundles().begin(); i != _body->row_bundles().end(); ++i) {
+	for (ARDOUR::BundleList::const_iterator i = r.begin(); i != r.end(); ++i) {
 		for (uint32_t j = 0; j < (*i)->nchannels(); ++j) {
 
-			uint32_t x = 0;
+			double x = 0;
 			if (_location == LEFT) {
-				x = _longest_bundle_name + name_pad() * 2;
+				x = _longest_bundle_name + _highest_group_name + name_pad() * 4;
 			} else if (_location == RIGHT) {
 				x = 0;
 			}
 
-			Gdk::Color const colour = get_a_bundle_colour (i - _body->row_bundles().begin ());
+			Gdk::Color const colour = get_a_bundle_colour (i - r.begin ());
 			set_source_rgb (cr, colour);
 			cairo_rectangle (
 				cr,
@@ -154,7 +211,7 @@ PortMatrixRowLabels::render (cairo_t* cr)
 
 			cairo_text_extents_t ext;
 			cairo_text_extents (cr, (*i)->channel_name(j).c_str(), &ext);
-			uint32_t const off = (row_height() - ext.height) / 2;
+			double const off = (row_height() - ext.height) / 2;
 
 			set_source_rgb (cr, text_colour());
 			cairo_move_to (cr, x + name_pad(), y + name_pad() + off);
@@ -187,8 +244,9 @@ PortMatrixRowLabels::button_press (double x, double y, int b, uint32_t t)
 
 		boost::shared_ptr<ARDOUR::Bundle> bundle;
 		uint32_t channel = 0;
-		
-		for (std::vector<boost::shared_ptr<ARDOUR::Bundle> >::const_iterator i = _body->row_bundles().begin(); i != _body->row_bundles().end(); ++i) {
+
+		ARDOUR::BundleList const r = _body->row_ports().bundles();
+		for (ARDOUR::BundleList::const_iterator i = r.begin(); i != r.end(); ++i) {
 			if (row < (*i)->nchannels ()) {
 				bundle = *i;
 				channel = row;
diff --git a/gtk2_ardour/port_matrix_row_labels.h b/gtk2_ardour/port_matrix_row_labels.h
index dd3d2a9348..dff6b71d26 100644
--- a/gtk2_ardour/port_matrix_row_labels.h
+++ b/gtk2_ardour/port_matrix_row_labels.h
@@ -54,8 +54,9 @@ private:
 	void rename_channel_proxy (boost::weak_ptr<ARDOUR::Bundle>, uint32_t);
 
 	PortMatrix* _port_matrix;
-	uint32_t _longest_port_name;
-	uint32_t _longest_bundle_name;
+	double _longest_port_name;
+	double _longest_bundle_name;
+	double _highest_group_name;
 	Gtk::Menu* _menu;
 	Location _location;
 };
diff --git a/libs/ardour/ardour/io.h b/libs/ardour/ardour/io.h
index a738519d57..1918a9a41a 100644
--- a/libs/ardour/ardour/io.h
+++ b/libs/ardour/ardour/io.h
@@ -127,8 +127,8 @@ class IO : public SessionObject, public AutomatableControls, public Latent
 	int connect_input_ports_to_bundle (boost::shared_ptr<Bundle>, void *src);
 	int connect_output_ports_to_bundle (boost::shared_ptr<Bundle>, void *src);
 
-	std::vector<boost::shared_ptr<Bundle> > bundles_connected_to_inputs ();
-	std::vector<boost::shared_ptr<Bundle> > bundles_connected_to_outputs ();
+	BundleList bundles_connected_to_inputs ();
+	BundleList bundles_connected_to_outputs ();
 
         boost::shared_ptr<Bundle> bundle_for_inputs () { return _bundle_for_inputs; }
         boost::shared_ptr<Bundle> bundle_for_outputs () { return _bundle_for_outputs; }
@@ -380,9 +380,6 @@ class IO : public SessionObject, public AutomatableControls, public Latent
 
 	void create_bundles_for_inputs_and_outputs ();
 	void setup_bundles_for_inputs_and_outputs ();
-
-	void maybe_add_input_bundle_to_list (boost::shared_ptr<Bundle>, std::vector<boost::shared_ptr<Bundle> >*);
-	void maybe_add_output_bundle_to_list (boost::shared_ptr<Bundle>, std::vector<boost::shared_ptr<Bundle> >*);
 };
 
 } // namespace ARDOUR
diff --git a/libs/ardour/ardour/session.h b/libs/ardour/ardour/session.h
index 2c173a9766..1a88882eb6 100644
--- a/libs/ardour/ardour/session.h
+++ b/libs/ardour/ardour/session.h
@@ -317,6 +317,10 @@ class Session : public PBD::StatefulDestructible
 	uint32_t ntracks () const;
 	uint32_t nbusses () const;
 
+	boost::shared_ptr<BundleList> bundles () {
+		return _bundles.reader ();
+	}
+
 	struct RoutePublicOrderSorter {
 	    bool operator() (boost::shared_ptr<Route>, boost::shared_ptr<Route> b);
 	};
@@ -771,7 +775,6 @@ class Session : public PBD::StatefulDestructible
 
 	/* I/O bundles */
 
-	void foreach_bundle (sigc::slot<void, boost::shared_ptr<Bundle> >);
 	void add_bundle (boost::shared_ptr<Bundle>);
 	void remove_bundle (boost::shared_ptr<Bundle>);
 	boost::shared_ptr<Bundle> bundle_by_name (string) const;
@@ -1616,9 +1619,7 @@ class Session : public PBD::StatefulDestructible
 
 	/* I/O bundles */
 
-	typedef list<boost::shared_ptr<Bundle> > BundleList;
-	mutable Glib::Mutex bundle_lock;
-	BundleList _bundles;
+	SerializedRCUManager<BundleList> _bundles;
 	XMLNode* _bundle_xml_node;
 	int load_bundles (XMLNode const &);
 
diff --git a/libs/ardour/ardour/types.h b/libs/ardour/ardour/types.h
index 53077387ed..cb058254bf 100644
--- a/libs/ardour/ardour/types.h
+++ b/libs/ardour/ardour/types.h
@@ -419,6 +419,9 @@ namespace ARDOUR {
 
 	typedef std::list<nframes64_t> AnalysisFeatureList;
 
+	class Bundle;
+	typedef std::vector<boost::shared_ptr<Bundle> > BundleList;
+  
 } // namespace ARDOUR
 
 std::istream& operator>>(std::istream& o, ARDOUR::SampleFormat& sf);
diff --git a/libs/ardour/io.cc b/libs/ardour/io.cc
index af4127c080..b86462472a 100644
--- a/libs/ardour/io.cc
+++ b/libs/ardour/io.cc
@@ -2629,42 +2629,11 @@ IO::create_bundles_for_inputs_and_outputs ()
         setup_bundles_for_inputs_and_outputs ();
 }
 
-/** Add a bundle to a list if is connected to our inputs.
- *  @param b Bundle to check.
- *  @param bundles List to add to.
- */
-void
-IO::maybe_add_input_bundle_to_list (boost::shared_ptr<Bundle> b, std::vector<boost::shared_ptr<Bundle> >* bundles)
-{
-	if (b->ports_are_outputs() == false) {
-		return;
-	}
-	
-	if (b->nchannels() != n_inputs().n_total ()) {
-		return;
-	}
-
-	for (uint32_t i = 0; i < n_inputs().n_total (); ++i) {
-
-		Bundle::PortList const & pl = b->channel_ports (i);
-
-		if (pl.empty()) {
-			return;
-		}
-
-		if (!input(i)->connected_to (pl[0])) {
-			return;
-		}
-	}
-
-	bundles->push_back (b);
-}
-
 /** @return Bundles connected to our inputs */
-std::vector<boost::shared_ptr<Bundle> >
+BundleList
 IO::bundles_connected_to_inputs ()
 {
-	std::vector<boost::shared_ptr<Bundle> > bundles;
+	BundleList bundles;
 	
 	/* User bundles */
 	for (std::vector<UserBundleInfo>::iterator i = _bundles_connected_to_inputs.begin(); i != _bundles_connected_to_inputs.end(); ++i) {
@@ -2672,51 +2641,31 @@ IO::bundles_connected_to_inputs ()
 	}
 
 	/* Normal bundles */
-	_session.foreach_bundle (
-		sigc::bind (sigc::mem_fun (*this, &IO::maybe_add_input_bundle_to_list), &bundles)
-		);
+	boost::shared_ptr<ARDOUR::BundleList> b = _session.bundles ();
+	for (ARDOUR::BundleList::iterator i = b->begin(); i != b->end(); ++i) {
+		if ((*i)->ports_are_outputs() == false || (*i)->nchannels() != n_inputs().n_total()) {
+			continue;
+		}
+
+		for (uint32_t j = 0; j < n_inputs().n_total(); ++j) {
+
+			Bundle::PortList const& pl = (*i)->channel_ports (j);
+			if (!pl.empty() && input(j)->connected_to (pl[0])) {
+				bundles.push_back (*i);
+			}
+
+		}
+	}
 
 	return bundles;
 }
 
 
-/** Add a bundle to a list if is connected to our outputs.
- *  @param b Bundle to check.
- *  @param bundles List to add to.
- */
-void
-IO::maybe_add_output_bundle_to_list (boost::shared_ptr<Bundle> b, std::vector<boost::shared_ptr<Bundle> >* bundles)
-{
-	if (b->ports_are_inputs() == false) {
-		return;
-	}
-
-	if (b->nchannels () != n_outputs().n_total ()) {
-		return;
-	}
-
-	for (uint32_t i = 0; i < n_outputs().n_total (); ++i) {
-
-		Bundle::PortList const & pl = b->channel_ports (i);
-
-		if (pl.empty()) {
-			return;
-		}
-
-		if (!output(i)->connected_to (pl[0])) {
-			return;
-		}
-	}
-
-	bundles->push_back (b);
-}
-
-
 /* @return Bundles connected to our outputs */
-std::vector<boost::shared_ptr<Bundle> >
+BundleList
 IO::bundles_connected_to_outputs ()
 {
-	std::vector<boost::shared_ptr<Bundle> > bundles;
+	BundleList bundles;
 
 	/* User bundles */
 	for (std::vector<UserBundleInfo>::iterator i = _bundles_connected_to_outputs.begin(); i != _bundles_connected_to_outputs.end(); ++i) {
@@ -2724,9 +2673,21 @@ IO::bundles_connected_to_outputs ()
 	}
 
 	/* Auto bundles */
-	_session.foreach_bundle (
-		sigc::bind (sigc::mem_fun (*this, &IO::maybe_add_output_bundle_to_list), &bundles)
-		);
+	boost::shared_ptr<ARDOUR::BundleList> b = _session.bundles ();
+	for (ARDOUR::BundleList::iterator i = b->begin(); i != b->end(); ++i) {
+		if ((*i)->ports_are_inputs() == false || (*i)->nchannels() != n_outputs().n_total()) {
+			continue;
+		}
+
+		for (uint32_t j = 0; j < n_outputs().n_total(); ++j) {
+
+			Bundle::PortList const& pl = (*i)->channel_ports (j);
+
+			if (!pl.empty() && output(j)->connected_to (pl[0])) {
+				bundles.push_back (*i);
+			}
+		}
+	}
 
 	return bundles;	
 }
diff --git a/libs/ardour/session.cc b/libs/ardour/session.cc
index f870a677dc..59b873e87f 100644
--- a/libs/ardour/session.cc
+++ b/libs/ardour/session.cc
@@ -138,6 +138,7 @@ Session::Session (AudioEngine &eng,
 	  routes (new RouteList),
 	  auditioner ((Auditioner*) 0),
 	  _total_free_4k_blocks (0),
+	  _bundles (new BundleList),
 	  _bundle_xml_node (0),
 	  _click_io ((IO*) 0),
 	  click_data (0),
@@ -219,6 +220,7 @@ Session::Session (AudioEngine &eng,
 	  routes (new RouteList),
 	  auditioner ((Auditioner *) 0),
 	  _total_free_4k_blocks (0),
+	  _bundles (new BundleList),
 	  _bundle_xml_node (0),
 	  _click_io ((IO *) 0),
 	  click_data (0),
@@ -3761,8 +3763,9 @@ void
 Session::add_bundle (shared_ptr<Bundle> bundle)
 {
 	{
-		Glib::Mutex::Lock guard (bundle_lock);
-		_bundles.push_back (bundle);
+		RCUWriter<BundleList> writer (_bundles);
+		boost::shared_ptr<BundleList> b = writer.get_copy ();
+		b->push_back (bundle);
 	}
 
 	BundleAdded (bundle); /* EMIT SIGNAL */
@@ -3776,11 +3779,12 @@ Session::remove_bundle (shared_ptr<Bundle> bundle)
 	bool removed = false;
 
 	{
-		Glib::Mutex::Lock guard (bundle_lock);
-		BundleList::iterator i = find (_bundles.begin(), _bundles.end(), bundle);
+		RCUWriter<BundleList> writer (_bundles);
+		boost::shared_ptr<BundleList> b = writer.get_copy ();
+		BundleList::iterator i = find (b->begin(), b->end(), bundle);
 
-		if (i != _bundles.end()) {
-			_bundles.erase (i);
+		if (i != b->end()) {
+			b->erase (i);
 			removed = true;
 		}
 	}
@@ -3795,9 +3799,9 @@ Session::remove_bundle (shared_ptr<Bundle> bundle)
 shared_ptr<Bundle>
 Session::bundle_by_name (string name) const
 {
-	Glib::Mutex::Lock lm (bundle_lock);
-
-	for (BundleList::const_iterator i = _bundles.begin(); i != _bundles.end(); ++i) {
+	boost::shared_ptr<BundleList> b = _bundles.reader ();
+	
+	for (BundleList::const_iterator i = b->begin(); i != b->end(); ++i) {
 		if ((*i)->name() == name) {
 			return* i;
 		}
@@ -4290,12 +4294,4 @@ Session::sync_order_keys (const char* base)
 	Route::SyncOrderKeys (base); // EMIT SIGNAL
 }
 
-void
-Session::foreach_bundle (sigc::slot<void, boost::shared_ptr<Bundle> > sl)
-{
-	Glib::Mutex::Lock lm (bundle_lock);
-	for (BundleList::iterator i = _bundles.begin(); i != _bundles.end(); ++i) {
-		sl (*i);
-	}
-}
 
diff --git a/libs/ardour/session_state.cc b/libs/ardour/session_state.cc
index 6c6ce18c8b..42dae522df 100644
--- a/libs/ardour/session_state.cc
+++ b/libs/ardour/session_state.cc
@@ -1061,8 +1061,8 @@ Session::state(bool full_state)
 	
 	child = node->add_child ("Bundles");
 	{
-		Glib::Mutex::Lock lm (bundle_lock);
-		for (BundleList::iterator i = _bundles.begin(); i != _bundles.end(); ++i) {
+		boost::shared_ptr<BundleList> bundles = _bundles.reader ();
+		for (BundleList::iterator i = bundles->begin(); i != bundles->end(); ++i) {
 			boost::shared_ptr<UserBundle> b = boost::dynamic_pointer_cast<UserBundle> (*i);
 			if (b) {
 				child->add_child_nocopy (b->get_state());