this happenned twice when i was calibrating my battery, and again at around 20%. i have not bled the mbp lower than those two instances, but it seems a little more than coincidence, yes? In fact the first time i calibrated, i could never get it to give me the 'low bat warning' (which i think its supposed to?) it just kept on getting the grey screen and restart dialogue. is anyone else experiencing this? i just wanted to check, i will test it again when i have time.