mplayer freezes when toggling full size ('f')

I play videos from Konsole using mplayer.

Often (but not always), when I try to toggle the full size (with the key 'f') mplayer will freeze, the output will freeze, and the red button to close the konsole tab will disappear...

Using Kubuntu 11.04, nvidea drivers (geforce 960GSO) with 3D desktop effects.