These steps should be easy to reproduce.
[LIST=1]
[*]Load up ZC, and make sure it's on Windowed.
[*]Start playing any ZC Quest. (I used Classic here)
[*]While playing, hit the escape button to bring up the menu. Note that the music has been silenced.
[*]Click anywhere out of ZC's window.
[*]Click back on ZC's Window.
[*]TADA! You hear music when you shouldn't.
[/LIST]
Are there any other Mac users that can help confirm this?