https://bugs.freedesktop.org/show_bug.cgi?id=110635
--- Comment #1 from Timothy Arceri t_arceri@yahoo.com.au --- Looks like it might be the same as bug #110575.
Do either of these go away when you run steam with the following:
R600_DEBUG=zerovram steam
Or setting the launch options for the game in steam to:
R600_DEBUG=zerovram %command%