Yes, I am seeing the exact same thing.
Ive just updated to a core i5 Mac Mini, so I am using fullscreen more than on my old Core2Duo mini from 2008 bcause the video is so much smoother, and found this issue with itunes. Really annoying as I like full screen because I can just swipe between the screens rather than having to go through Mission control or grabbing the keyboard for a "Command-Tab" app switch.
However if you take the video out of full screen, iTunes keeps it full screen, but you get the iTunes bar top and bottom. When closing this video, it does return to iTunes fullscreen OK.
Annoying feature I think 8)