I did all the initial testing on shutdown with internal vs. external power sources. I only tested firmware 1.32.02 It always shut down properly with internal batteries but I did get caught once in a different way...
If you pause a recording and then press play again, it resumes recording - it just appends to the same track.
If you are recording and press 'stop', it will close the track and then return to a 'record pause' mode.
From here, if you hold the play button it will start recording a new track, but if you just press play quickly, it will simply play back the previously recorded track, then go into idle, then shut down.
Of course after the fact you can't really tell what happened. There was a time I did this, then later glanced down and realized it was playing back the opening act instead of recording the headliner!
So 2 questions:
Did you have some battery power left when you got home and powered it up?
Did you press stop between sets or anything like that?