I noticed this yesterday, when my battery was completely drained (phone shut down). Usually, my battery is almost drained during the day because I use the phone none stop for at least 8hrs. When I got home yesterday, I put th Pre on the touchstone and it started charging, first by displaying a huge battery sign, then displaying the usual Pre screen. About an hour later, it was fully charged. When I took it off the stone, 5min later the phone rebooted by itself. It was sitting on the desk when this happened, immobile.

Now, this is not the first time it occurs. It happened to myself with a previous phone, that had the battery depleted completely and came off the touchstone. Honestly, I cannot remember exactly the time it took until the phone "decided" to reboot, but it was pretty short, into both phones.