https://bugs.freedesktop.org/show_bug.cgi?id=72291
--- Comment #6 from Dieter Nützel Dieter@nuetzel-hh.de --- (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 ;-)