My phone was running hot, so I decided to shut it down to cool. Instead of shutting down, though, it rebooted. When it was done, I waited a minute, and tried again. Reboot. Again. Reboot. Finally, decided to try a soft reset and that seemed to fix it. This isn't the first time it decided not to shutdown and restarted instead, but first time it did it three times in a row. At least the soft reset worked. 1520 on 8.1 DP -- hoping the "official" rollout takes care of these little issues.