Help Sleep mode

The other night I got a low space warning. I was in my manage applications setting and clearing some data. Since then my phone will not go into a sleep mode of sorts.

Usually if I hit the button that turns my screen off, if I then hit home it would be sleeping / locked and I'd swipe / slide to open the screen. If I got a text or call, I'd also swipe to the left or right to open it up.

Now when I hit the button to turn the screen off it turns off but if I hit home my screen is immediately opened and unlocked. So I have no protection from pocket dialing etc now.

I have gone through every setting on the phone that I can think of, and cannot figure out how to put it back the way it was. Any help would be greatly appreciated.