I have this here as well (choosing "Log Out" OR the new "Shut Down" menu item crashes gnome-panel). Can we change to a more explicit bug title, such as "Crash when logging out or shutting down from system menu" ?

I recompiled gnome-panel to get the bt, here it is, for example when choosing "Shut Down" :

(gdb) run
Starting program: /home/manu/dev/gnome-panel-2.13.5/gnome-panel/gnome-panel
[Thread debugging using libthread_db enabled]
[New Thread -1224079680 (LWP 474)]
[New Thread -1227699280 (LWP 492)]

Gtk-ERROR **: file gtkmessagedialog.c: line 244 (gtk_message_dialog_get_message_type): should not be reached
aborting...

Program received signal SIGTRAP, Trace/breakpoint trap.
[Switching to Thread -1224079680 (LWP 474)]
0xb76d0957 in g_logv () from /usr/lib/libglib-2.0.so.0
(gdb) bt
#0  0xb76d0957 in g_logv () from /usr/lib/libglib-2.0.so.0
#1  0xb76d0c14 in g_log () from /usr/lib/libglib-2.0.so.0
#2  0xb76d0c80 in g_assert_warning () from /usr/lib/libglib-2.0.so.0
#3  0xb79c8677 in gtk_message_dialog_get_type () from /usr/lib/libgtk-x11-2.0.so.0
#4  0xb773a4ff in g_object_get_valist () from /usr/lib/libgobject-2.0.so.0
#5  0xb773a732 in g_object_get () from /usr/lib/libgobject-2.0.so.0
#6  0xb7f2896d in libgnomeui_module_info_get () from /usr/lib/libgnomeui-2.so.0
#7  0xb774553a in g_signal_stop_emission () from /usr/lib/libgobject-2.0.so.0
#8  0xb7747238 in g_signal_emit_valist () from /usr/lib/libgobject-2.0.so.0
#9  0xb7747589 in g_signal_emit () from /usr/lib/libgobject-2.0.so.0
#10 0xb7a9f3d6 in gtk_widget_show () from /usr/lib/libgtk-x11-2.0.so.0
#11 0xb7742663 in g_cclosure_marshal_VOID__VOID () from /usr/lib/libgobject-2.0.so.0
#12 0xb7735798 in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
#13 0xb7745715 in g_signal_stop_emission () from /usr/lib/libgobject-2.0.so.0
#14 0xb7747238 in g_signal_emit_valist () from /usr/lib/libgobject-2.0.so.0
#15 0xb7747589 in g_signal_emit () from /usr/lib/libgobject-2.0.so.0
#16 0xb7a992fd in gtk_widget_activate () from /usr/lib/libgtk-x11-2.0.so.0
#17 0xb79c60af in gtk_menu_shell_activate_item () from /usr/lib/libgtk-x11-2.0.so.0
#18 0xb79c6381 in gtk_menu_shell_activate_item () from /usr/lib/libgtk-x11-2.0.so.0
#19 0xb79bcb34 in gtk_menu_reorder_child () from /usr/lib/libgtk-x11-2.0.so.0
#20 0xb79b7440 in _gtk_marshal_BOOLEAN__BOXED () from /usr/lib/libgtk-x11-2.0.so.0
#21 0xb7735165 in g_cclosure_new_swap () from /usr/lib/libgobject-2.0.so.0
#22 0xb7735798 in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
#23 0xb7745e6e in g_signal_stop_emission () from /usr/lib/libgobject-2.0.so.0
#24 0xb7746f94 in g_signal_emit_valist () from /usr/lib/libgobject-2.0.so.0
#25 0xb7747589 in g_signal_emit () from /usr/lib/libgobject-2.0.so.0
#26 0xb7a994df in gtk_widget_activate () from /usr/lib/libgtk-x11-2.0.so.0
#27 0xb79b5bbd in gtk_propagate_event () from /usr/lib/libgtk-x11-2.0.so.0
#28 0xb79b5fcb in gtk_main_do_event () from /usr/lib/libgtk-x11-2.0.so.0
#29 0xb7859c1c in _gdk_events_queue () from /usr/lib/libgdk-x11-2.0.so.0
#30 0xb76c8547 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#31 0xb76cb606 in g_main_context_check () from /usr/lib/libglib-2.0.so.0
#32 0xb76cb928 in g_main_loop_run () from /usr/lib/libglib-2.0.so.0
#33 0xb79b52c5 in gtk_main () from /usr/lib/libgtk-x11-2.0.so.0
#34 0x08066837 in main (argc=0, argv=0x0) at main.c:84
(gdb)