Comment 12 for bug 408293

I forwarded this bug upstream to https://bugs.freedesktop.org/show_bug.cgi?id=23104 - I'd encourage you to subscribe to that.

They indicate that this is probably fixed by a couple xserver commits. I'm going to give a shot to seeing if it'd be hard to backport those to our 1.6.3 xserver, otherwise you may want to test using a newer xserver snapshot, which can be found in the xorg-edgers ppa. https://edge.launchpad.net/~xorg-edgers/+archive/ppa