https://bugs.freedesktop.org/show_bug.cgi?id=82201
--- Comment #38 from Sebastian Parborg darkdefende@gmail.com --- Kai, I have an 290x and I'm having the same problem as you.
However I do not have windows installed at all. So I think we can rule that one out.
For me it seem like the card loses the ability to reclock after a while. However I have regained the reclocking ability by rebooting to use fgrlx and then reboot back to use radeon...
I'm just as confused as you are why it stops working. :S