diff --git a/libs/ardour/io.cc b/libs/ardour/io.cc
index f535467cbe..b5a81c71e8 100644
--- a/libs/ardour/io.cc
+++ b/libs/ardour/io.cc
@@ -89,6 +89,8 @@ IO::~IO ()
 {
 	Glib::Threads::Mutex::Lock lm (io_lock);
 
+	DEBUG_TRACE (DEBUG::Ports, string_compose ("IO %1 unregisters %2 ports\n", name(), _ports.num_ports()));
+
 	BLOCK_PROCESS_CALLBACK ();
 
 	for (PortSet::iterator i = _ports.begin(); i != _ports.end(); ++i) {
diff --git a/libs/ardour/port_manager.cc b/libs/ardour/port_manager.cc
index f057b2ffa2..7a13756dab 100644
--- a/libs/ardour/port_manager.cc
+++ b/libs/ardour/port_manager.cc
@@ -56,6 +56,8 @@ PortManager::clear_pending_port_deletions ()
 {
 	Port* p;
 
+	DEBUG_TRACE (DEBUG::Ports, string_compose ("pending port deletions: %1\n", _port_deletions_pending.read_space()));
+
 	while (_port_deletions_pending.read (&p, 1) == 1) {
 		delete p;
 	}
@@ -406,6 +408,7 @@ PortManager::unregister_port (boost::shared_ptr<Port> port)
 		Ports::iterator x = ps->find (make_port_name_relative (port->name()));
 
 		if (x != ps->end()) {
+			DEBUG_TRACE (DEBUG::Ports, string_compose ("removing %1 from port map (uc=%2)\n", port->name(), port.use_count()));
 			ps->erase (x);
 		}