fix visual undo.

TODO: Check if it’s feasible/required to add a
GUIPropertiesChanged signal and have axis-views
subscribe to it.

gtk2_ardour/axis_view.h

@@ -75,6 +75,7 @@ class AxisView : public virtual Selectable, public PBD::ScopedConnectionList, pu
 	virtual bool set_marked_for_display (bool);
 
 	static GUIObjectState& gui_object_state();
+	void clear_property_cache() { property_hashtable.clear(); }
 	
   protected:
 

gtk2_ardour/editor.cc

@@ -4461,6 +4461,7 @@ Editor::use_visual_state (VisualState& vs)
 		*ARDOUR_UI::instance()->gui_object_state = *vs.gui_state;
 		
 		for (TrackViewList::iterator i = track_views.begin(); i != track_views.end(); ++i) {	
+			(*i)->clear_property_cache();
 			(*i)->reset_visual_state ();
 		}
 	}