Did you try to disable the compositing / desktop effects before open the video file?
I remember this issue from other posters - this might be it: http://smplayer.berlios.de/forums/viewtopic.php?id=979
But I doubt is your current issue since that was quite a while ago (2009). Hopefully disabling the compositing / desktop effects will work.
If you use cairo-dock, try disabling/closing it as they say here: https://bugs.launchpad.net/ubuntu/+sour ... bug/507716
If that's the issue seems the qt-devs do not want / have time to fix the issue (more than 1 year without a response): http://www.qtforum.org/article/26669/qt ... ntext.html
Cheers.