Comment 33 for bug 481656

Do I understand correctly that the app crashes only on ibus daemon restart?

You are probably right about this being an ibus issue. This might be related:
http://code.google.com/p/ibus/issues/detail?id=593

With a fix posted late Nov/09 and ibus making fairly frequent releases, there's a good chance that this fix has made it into F12 by now. Is this still happening for you?