"system" reboots my device after I allow it to in SuperUser? Today, a random SuperUser request from "system", with UID 1000, appear. I figured that it was nothing, so I accepted it. A couple of seconds later, my phone rebooted, or at least that's what I think it did. I saw the T-Mobile screen flash by really quickly; the Samsung screen did not appear. So, what happened and should I be concerned?
If you've installed any task killer application that has super user permission granted, this might be killing all the tasks(including system critical processes) which might result in a restart. 
An eg. for this would be ZDBox. 
Try checking if that's causing the problem.