Just came across an issue with restarting media in the Nov CTP.  First off, assume the code is using independent mode.  (See the draft of the what's new article for more on media in the Nov CTP and the difference between independent mode and clock mode.) Let's say you have a movie or sound that you want to replay.  Ideally, once you received the MediaEnded event or on some other event, you could call Play() and it would automatically "rewind" and play for you, such as what most players do. 

player.Play();

Not the case. So you might think, okay, I'll set the position of the MediaPlayer back to zero and then invoke Play() again, like this

player.Position = Timespan.Zero;
player.Play();

However, this also fails.  But, if you explicitly Stop() the media and then rewind and then call Play, everything will work:

player.Stop();
player.Position = Timespan.Zero;
player.Play();

By the time the product ships, the expected behavior will work, but those of you playing with the CTP, please keep this in mind!