http://bugs.winehq.org/show_bug.cgi?id=12861
--- Comment #11 from Matteo Modesti mattemod@gmail.com 2008-05-27 12:38:41 --- I thought it was a Gtk# problem and in that case it would've been related to Mono.
So you confirm that is a Gtk+ issue and not a Gtk# one? (sorry but actually i don't have any free time to test and confirm it myself)