I haver verified Roger's patch does indeed fix the problem on Linux CentOS 6.4 with IDLE 3.4.
The Linux situation is complex. Basically as I see it over the years pure X11 applications are becoming extinct and most developers either use GTK (for GNOME) or QT (for KDE). I don't blame anybody for moving to one of these toolkits because writing a pure X11 application is painful. In the near future Wayland http://en.wikipedia.org/wiki/Wayland_(display_server_protocol) will take over and I wonder how many X11 applications will actually be ported. I agree with Roger we should try and make IDLE as consistent as possible across operating systems.
+1 for applying the patch.