Comment 7 for bug 714280

This should be fixed by http://cgit.freedesktop.org/mesa/mesa/commit/?id=cbe9fc12a64c3ae89fd1b20e9e165aa4b76293a5 in mesa, work around for xorg-server at http://patchwork.freedesktop.org/patch/3987/
There's a couple other patches for mesa in the same vein that should go with that, AFAIK they're all cherry-picked to the 7.10 branch.
You may also want http://patchwork.freedesktop.org/patch/3986/ and http://patchwork.freedesktop.org/patch/3985/ in your X server.