For some reason, my Windows 7 (Ultimate, 64bit) laptop will not power off the display and keep it off if I have the screen saver and/or the timed auto-lock enabled. Either the display blanks (and locks) but never powers off, or it powers off for less then a minute, then the back light visibly powers back on and stays on, even though the screen remains blanked until I touch a key or the trackpad.
I've tried varying the screen power down time to greater than, less than, and exactly equal to the blank screen/lock time, with no success.
Turning the screen saver and the timed auto-lock off does allow the timed display power down in the power settings to work properly.
(Note that I am not talking about system sleep or hibernate. I'm talking about when the machine remains running, but only the display should power down.)