(In reply to comment #4)
> I also experience this problem on my HD5770 card. As far as I can remember
> it existed back when the UVD code was first released.
> 
> The freeze happens when a majority of the video windows is moved to the
> other screen. I guess it has something to do with vsync being changed to the
> other screen.
> 
> I also run git of all relevant packages except the kernel and I use up to
> date radeon-ucode.

Which kernel are you running - 3.12.1/2?
Then please try 3.13-rc2.
3.12.x missing some UVD fixes from Cristain König, currently.

Works for me on RV730 AGP.
But APU is a nother thing at this time ;-)