Default Lockscreen, screen timeout modes CM 10.2.1

My lockscreen is no longer working and I have no idea why. I have a 2 min. screen timeout but when I wake up the Nook with the "N" button the screen is already unlocked (I do not have the selection checked that uses this button to unlock). It used to work fine but then more or less stopped. I've tried all kinds of combinations of settings. Sometimes it will work once after changes, but then it stops again.

I've just discovered I can manually lock the screen with a quick press of the power button. That works every time but is sort of beside the point. It should (used to) lock automatically when the screen goes off after 2 min.

And...what exactly are the "screen timeout modes"? Each of the two consists of 3 time intervals but there is no explanation or description of what they are/do. Originally they were unselected and I just had the 2 min timeout. So are these deepening levels of power saving (dim, off, sleep)?

I wish there were some kind of reference for the CM settings. It would really help a noob like me