Recently upgraded to 4.1.2 from Gingerbread on a GT-I9100. All OK except for a couple of things, the main one being that after the screen times out, it takes several minutes or longer to go to the lock screen. I can't be certain, but after the initial upgrade, I thought the lock screen activated within seconds, just like my son's GT-I9100 (also running 4.1.2) does now. I've compared all my settings with his but they all appear to be the same. Any suggestions what could be causing this?