I just tried smart Screen off. It appears to be a disaster. When I touch the screen to do something, the screen turn itself off and then back on. I opened the pattern security lock, the same thing happens again. I quickly uninstalled.
Is it possible that you were covering the proximity sensor? I actually turn it off when I am using teh pad for long periods of time, but it saves me the hassle of turning teh fonepad on and off, which I find inconvenient.