handcent notification sound

My current handcent notification sound won't stop playing after hitting "X" on pop-up window.

I've made it so when I hit "X", it doesn't mark my messages as "read".

If i change it back to mark messages as "read", and then hit "X" on the pop-up window when I receive a new message, the notification sound stops.

My question is this: How can I make my notification sound stop playing when I hit "X" without having my messages be marked as "read"?

P.S. I've searched the forums for similar problems and didn't find anything.

Thank you