Cooper - one of the things the X5 does is stop playing when you remove the headphone jack (just like an iPod). If the X5 isn't playing anything, and no buttons are pressed - after a while (not sure of the default time), it turns itself off (auto-shutoff) to conserve battery. You can adjust the auto shut-off time in 'settings'.
This might explain one of those shut downs anyway.
Sure. But I have auto shutoff set to 8 minutes and my 'relief' break (leaving my X5 unattended at a hotel lobby bar) was maybe 2 minutes. Something happened that was unusual that day.