Comment 9 for bug 724874

I have a very similar (maybe same) problem. My backtrace looks slightly different

(unity-window-decorator:9108): GLib-GObject-CRITICAL **: g_object_get_data: assertion `G_IS_OBJECT (object)' failed

Program received signal SIGSEGV, Segmentation fault.
0x0000000000415bab in ?? ()
(gdb) bt
#0 0x0000000000415bab in ?? ()
#1 0x0000003f2840e7fc in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
#2 0x0000003f28420019 in ?? () from /usr/lib/libgobject-2.0.so.0
#3 0x0000003f28429258 in g_signal_emit_valist ()
   from /usr/lib/libgobject-2.0.so.0
#4 0x0000003f2842941f in g_signal_emit () from /usr/lib/libgobject-2.0.so.0
#5 0x0000003f33c16d44 in ?? () from /usr/lib/libwnck-1.so.22
#6 0x0000003f33c173d4 in ?? () from /usr/lib/libwnck-1.so.22
#7 0x0000003f27042c2d in g_main_context_dispatch () from /lib/libglib-2.0.so.0
#8 0x0000003f27043418 in ?? () from /lib/libglib-2.0.so.0
#9 0x0000003f27043a5a in g_main_loop_run () from /lib/libglib-2.0.so.0
#10 0x0000003f2ed35827 in gtk_main () from /usr/lib/libgtk-x11-2.0.so.0
#11 0x00000000004097f2 in main ()
(gdb)

I can trigger it reliably sending a mail from thunderbird. When the submission window (with the progress bar) closes unity-window-decorator crashes in 10 out of 10 cases.