AT3 stops playing when streaming iMac's display sleeps

An odd problem and easy to bypass, but still annoying.

Streaming music from my iMac (Mountian Lion) to Apple TV it stops playing when the display goes to sleep. The computer isn't sleeping, just the display. The music won't restart where it left off by pressing play either, nothing happens if you press play. I have to go back to the album/artist and start over to get it to play. It's kind of an odd problem which I can avoid by setting the display to sleep after 1 minute but curious if this a bug or just a problem with my setup.