[belese]

i've got same problem, for ex you tube video,
it's quite simple to reproduce ,
i use the extension 'play to xbmc' for chrome, and queue 2 you tube videos from chrome,
this first one play fine, second one have only sound.
have to do stop, and restart video, and this is ok.
Sometimes it is good, don't check resolution, may be it's appear only on same resolution.

But i used the standard alpha 4, nothing updated except xbian-config