https://bugs.freedesktop.org/show_bug.cgi?id=64850
--- Comment #3 from Jakob Nixdorf flocke@shadowice.org --- Update:
I tested the Arch Linux kernels 3.9.2 and 3.8.11 with the same result.
And, in case it is important, I noticed this line in dmesg:
[ 3.169540] radeon 0000:01:00.0: Invalid ROM contents
I hope this can help further.