This is ridiculous...
So I deployed 10.3.1 to my users today, giving them the reboot prompt.. got a few calls saying their computer reboots on its own. I figured they were ignoring the prompt and letting the 5 mins go, which then auto-reboots. But, decided to test it myself after an irate user called.. Refreshed device, update started with percentage in the balloon in systray. Update finished, Prompt came up.. I hit "cancel" (do not reboot right now) , and sure enough... all my programs closed and my computer restarted.

UGH!!!!!!!!!!!!!!