The crash happened under no special circumstance. All applications were closed (pure desktop). Last closed App was Firefox. With some delay, apport popped up and redirected to this page.
edit:
The machine is a HP EliteBook 2760p running wily which has been updated stepwise from 12.4LTS.
See the crash dump file attached to comment #1.
upstart.unity-panel-service.log:
(unity-panel-service:1769): Indicator-Appmenu-CRITICAL **: menus_destroyed: assertion 'IS_WINDOW_MENU(wm)' failed
(unity-panel-service:1769): Indicator-Appmenu-CRITICAL **: menus_destroyed: assertion 'IS_WINDOW_MENU(wm)' failed
(unity-panel-service:1769): Indicator-Appmenu-CRITICAL **: menus_destroyed: assertion 'IS_WINDOW_MENU(wm)' failed
(unity-panel-service:1769): Indicator-Appmenu-CRITICAL **: menus_destroyed: assertion 'IS_WINDOW_MENU(wm)' failed
(unity-panel-service:1769): GLib-CRITICAL **: Source ID 140 was not found when attempting to remove it
(unity-panel-service:1769): Indicator-Appmenu-CRITICAL **: window_menu_model_new: assertion 'BAMF_IS_APPLICATION(app)' failed
(unity-panel-service:1769): Indicator-Appmenu-CRITICAL **: track_menus: assertion 'IS_WINDOW_MENU(menus)' failed
(unity-panel-service:1769): GLib-CRITICAL **: Source ID 928 was not found when attempting to remove it
(unity-panel-service:1769): Indicator-Appmenu-WARNING **: Already have a menu for window ID 62914763 with path /com/canonical/menu/3C000CB from :1.87, unregistering that one
(unity-panel-service:1769): Indicator-Appmenu-CRITICAL **: window_menu_model_new: assertion 'BAMF_IS_APPLICATION(app)' failed
(unity-panel-service:1769): Indicator-Appmenu-CRITICAL **: track_menus: assertion 'IS_WINDOW_MENU(menus)' failed
(unity-panel-service:1769): GLib-CRITICAL **: Source ID 944 was not found when attempting to remove it
(unity-panel-service:1769): Indicator-Appmenu-WARNING **: Already have a menu for window ID 62914763 with path /com/canonical/menu/3C000CB from :1.90, unregistering that one
(unity-panel-service:2854): Indicator-Appmenu-CRITICAL **: window_menu_model_new: assertion 'BAMF_IS_APPLICATION(app)' failed
(unity-panel-service:2854): Indicator-Appmenu-CRITICAL **: track_menus: assertion 'IS_WINDOW_MENU(menus)' failed
(unity-panel-service:2854): Indicator-Appmenu-WARNING **: Already have a menu for window ID 62914763 with path /com/canonical/menu/3C000CB from :1.90, unregistering that one
(unity-panel-service:2854): Indicator-Appmenu-CRITICAL **: window_menu_model_new: assertion 'BAMF_IS_APPLICATION(app)' failed
(unity-panel-service:2854): Indicator-Appmenu-CRITICAL **: track_menus: assertion 'IS_WINDOW_MENU(menus)' failed
(unity-panel-service:2854): GLib-CRITICAL **: Source ID 143 was not found when attempting to remove it
Nobody here to give me a hint how to correctly upload a .crash file?
Knowingly it's not pretty, because all data are cluttered together in the same file, here it is ...