This has been a problem with the more recent versions.
If I'm watching a movie on one screen and drag it to another it's always been a bit temperamental, sometimes the video goes blank until it's returned to it's original screen.
It's gotten much more obnoxious, however. These days if I drag a screen there's a good chance I end up with a frozen image, and if the video is a high def that goes clear across my 1280x1024 monitor the odds are virtually 100%.
Note that the program is *NOT* frozen, the movie continues to play but doesn't update it's screen.
If I pause the movie and move it the screen is still frozen but it's not as bad as maximizing it and then restoring it to normal appears to always get it back in operation. (Note that this is done while it's still paused.)