Bug#564880: xserver-xorg-video-radeon: fails to properly handle, enlargement of vertical screen size
Have you also tried to take a screenshot with Gimp. using the "Select
whole Screen" option?
I'm asking because I have a corruption that looks similar to your
screenshot and could be fixed by ColorTiling=off, but I was able take a
screenshot with the Gimp, and I'd like to know whether it's the same issue.
I can see this issue after returning from some screen-resing game (I'Ve
tried ppracer). The issue also occurs when I manually resize my screen
with xrandr ("1280x1024" > "800x600" > "1280x1024"), but then the
corruption is not immeadiatly visible.