Ok, I will do that...
That sounds like a GTK+ bug. Please add a test case to bugzilla, ideallyin C.Ooops! I have no experience in GTK+ / C ... :-/_ideally_. That means you can open a gtkmm bug report with a c++ as-simple-as-possible test case first and Murray will press you and everyone of us to translate it into c so that we can reassign the bug to gtk ...