Jeremy Huddleston wrote:

Based on your stack trace, my guess is that you're hitting this:

http://lists.x.org/archives/xorg-devel/2011-May/022281.html

Would you mind filing a bug report, so I can track the fix getting in to XQuartz?

That post gives me a better idea of what I might do to reproduce the error. Let me take a closer look at trying to reproduce it. If I can't, there's no way I can track the bug's progress or confirm fixes. -Dave