Comment # 3 on bug 93471 from Michel Dänzer

Any chance you could try the current xf86-video-ati release 7.6.1?
http://cgit.freedesktop.org/xorg/driver/xf86-video-ati/commit/?id=ddaba449e8d6fe9fc0d97085e4045843fd8d7af9
might help.