Index: trunk/src/org/openstreetmap/josm/gui/layer/OsmDataLayer.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/layer/OsmDataLayer.java	(revision 14536)
+++ trunk/src/org/openstreetmap/josm/gui/layer/OsmDataLayer.java	(revision 14537)
@@ -1060,4 +1060,7 @@
         data.removeHighlightUpdateListener(this);
         removeClipboardDataFor(this);
+        if (!data.isLocked()) {
+            data.clear();
+        }
     }