I noticed the very same thing recently (n800, Diablo, running latest updates). I had some headphones plugged in and as soon as I removed them it muted the sound for the headphones (I would assume so since I unplugged them) but I got nothing from the speakers. Plugging them back in gave me sound in them, but nothing I could do short of rebooting gave me sound from the speakers. I'm using an A2DP-patched kernel and bluez-utils and I'm wondering if this has caused the problem.

Larry