Volume up/down latency issue - and no sound - in clamshell mode

I have a late '08 MBP hooked up to a new 27" ACD, using a bluetooth apple keyboard and magic mouse.

It's been working fine in all respects until I woke it up today. Everything is fine except the volume. If I tap volume up or down on the keyboard, there's serious latency (5-10 seconds) between me pressing the button and it showing the volume moving. Secondly (and more importantly), there's no sound at all (no matter what volume it's set at). I've already directed the sound through the monitor's speakers (like I said, everything was working just fine).

I've tried rebooting, double-checking the sound settings, and disconnecting/reconnecting the bluetooth keyboard.

I'm not sure what else to do. Any ideas??

 

Audio goes through the USB cable.

Side note: According the guys at the Mac Store, even if you have a new MBP that DOES support sound through the MDP, you STILL have to use the USB cable for other functions.

I disconnected and reconnected the monitor, nothing. Then rebooted the computer open, connected the bluetooth mouse/keyboard, closed the lid, hooked up the monitor, awoke it, and it worked.

Puzzling. I still can't figure out why it did it though.