This problem had been reported before. But it's really hard to reproduce.
I will try to investigate further on this. If you have some additional information that could help to reproduce the behaviour, please inform me in a private email (wolo@wolosoft.com) or use the bug report form (on the left).
I had this happen to me tonight with a Win2000 Pro setup. The Dr Watson Logfile showed that media player had an access violation. I had just upgraded to Media Player 9.