This was tested with a AMD Radeon HD 6950.
Good image (random screenshot taken from youtube) :
http://picload.org/image/carrior/good.png
Bad image (rendered with r600g) :
http://img5.picload.org/image/carrpgi/2014-10-28_00001.jpg

I'm not the only one with this problem, people are talking about it at phoronix
(
http://www.phoronix.com/forums/showthread.php?108025-Dead-Island-GOTY-Now-Available-On-Linux-SteamOS
), in the steam forums (
http://steamcommunity.com/app/91310/discussions/0/613940109818649734/ ) and at
other places.

Playing around with SB, HyperZ and LLVM didn't change anything (except LLVM
which freezes the game before anything is painted to the screen).

If there's anything I can do to help tracking this down feel free to ask for
it.