I was using combination, I have just switched to single key, and it also sometimes shows a key pressed when it first starts up. Clock is still working, so if it only had a timeout for the keypress, or if the timeout worked a bit better. I notice that it does this more often when I lock the phone with the lock attached to a button more than just using the power buttion to shut it down.

** update ** Since I have lock and turn off screen enabled, I think it is hanging on the same button I use to lock the phone.