Index: /trunk/src/org/openstreetmap/josm/gui/MainApplication.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/MainApplication.java	(revision 12132)
+++ /trunk/src/org/openstreetmap/josm/gui/MainApplication.java	(revision 12133)
@@ -315,5 +315,7 @@
                 !args.hasOption(Option.NO_MAXIMIZE) && Main.pref.getBoolean("gui.maximized", false));
         final MainFrame mainFrame = new MainFrame(geometry);
-        Main.contentPanePrivate = (JComponent) mainFrame.getContentPane();
+        if (mainFrame.getContentPane() instanceof JComponent) {
+            Main.contentPanePrivate = (JComponent) mainFrame.getContentPane();
+        }
         Main.mainPanel = mainFrame.getPanel();
         Main.parent = mainFrame;