I have this problem as well. I can find the video playing if I enter KDE but I just get a black screen with audio within LMCE.
I switched to UI2 and got back the video, then back to UI3 and the video was gone again...
Is there anyway to force start of the xcompmanager? Can it be manually started in a shell window in case it isn't automatically started on boot?
I am just now switching back to UI2, will try to switch back to UI3 once more after that and then see if xcompmgr can be started in some other way if it doesn't work...