I'm experiencing some strange behaviour from Internet explorer, it can be seen here: SoundOut
If following any link on the site causes the IE window to move to the background, this is easiest to see if you have some other app maximised behind IE.
If you wait a few seconds then it jumps back to the front.
I have no idea why it does this and no other browser shows the same behaviour. As you can imagine, this causes some usability issues.
I'm using windows 7 (64 bit) and have IE9 for testing but the same behaviour has been reported by users of IE7 and IE8.