In all the time I have had my empeg, (Mark I, II and IIa all grouped togther), it has happened once. I know for sure the empeg went into standby when it happened, and based on the position in the playlist, it started playing again before my standby timeout ot 15 minutes expired.

I never figured out the cause, and haven't seen it happen again. Lowering the standby of my player would probably greatly decrease the chances of it happening again.