I know there's a lot of advice for MacBooks randomly shutting down or restarting, but my question is a bit different. My MacBook Pro (mid-2010 15") only turns off when I instruct it to. However, it will only ever Restart: If "Shutdown" is chosen, it will instead restart. If "Sleep" is chosen, it will restart. If I close the lid and the computer tries to go to sleep, it will restart. The only way to get it to power off is by manually holding the power button.
The issue began when I updated to 10.8.4 so I assume it's some sort of software problem with the OS (could a .plist file have been changed somewhere with a bizarre value?). I was hoping that upgrading to 10.8.5 might help, but it's impossible to update because...the computer reset required prohibits the update from happening.
I've also checked the kernel's shutdown causes, and it's typically code "3" or "-60" I know there's no guide to what these mean, but I'm guessing they refer to the system restarting on its own ("3") and being turned off manually by the user ("-60") but I have nothing to back that up.
What might cause a Mac to display this behavior?