It's not a warm up, it *is* the "play after ignition off" feature. It was mentioned in the 12a release notes, I believe.

After accessory goes off, the empeg goes to sleep. You can wake it at any time with buttons or remote, and it will carry on operating. If you don't wake it within 60 seconds (or, after waking it you power off) the until will go to sleep totally, and will only wake up if the ignition comes on or a timer event (not implemented yet ;) ) happens.

Hugo