Comment # 21 on bug 69341 from langkamp@tomblog.de

did you tried a recent git version? 
you also could try the oibaf ppa with (k)ubuntus - you wrote you tested only
plain kubuntu. 
Maybe you also have to set radeon.dpm=1 in grub. I have not tested without it.

in the end it could also be a opensuse thing (but i don´t believe that) or a
hardware fault (I have an gibabyte OC version)

my best guess at the moment is radeon.dpm=1