I'm using "ati-dri 8.0.2" and I encounter artifacts like this:
when using cairo (compiled with xcb-support) and the default radeon settings.
If I disable "EAXPixmaps" support in my xorg.conf everything is fine.
I realized the glitches in firefox and awesome window manager (in the top panel).
This was also with cairo-xcb 1.10 (and ati-dri 7.11) an issue for me but since yesterday's update to 1.12 the glitches come more frequently (browsing is more or less impossible with enabled EAXPixmaps support).
Since I don't know whether this is cairo's or radeon's fault I'm opening a bug report here as well as in the radeon bug tracker.
*** This bug has been marked as a duplicate of bug 47266 ***