when destroying an ArdourDialog, be sure the Keyboard object knows about it.

It seems that there are ways to destroy a window without it emitting focus out

gtk2_ardour/ardour_dialog.cc

@@ -60,6 +60,7 @@ ArdourDialog::~ArdourDialog ()
                         spl->pop_front();
                 }
         }
+        Keyboard::the_keyboard().focus_out_window (0, this);
         WM::Manager::instance().remove (proxy);
 }