Comment 72 for bug 565883

I have uploaded a test package for xserver-xorg-video-ati in https://launchpad.net/~xorg-edgers/+archive/drivers-only
Please try it, although I am not sure if the kernel must be fixed as well for you to see a difference.

Reference to kernel patch: http://lists.freedesktop.org/archives/dri-devel/2010-April/000214.html