Comment 6 for bug 1291365

I tried some different conditions with Screen Turn-off time-out and Lock settings, and I found the problem is not for the lock delay time, but for screen turn-off.

When you manually lock the screen and thescreen turn-off time-out passed, you will get the blank screen after unlocking; because the Unity lock screen has prevented the screen to go blank.
So if you have “never” for screen turn-off, or unlock before the time-out reaches, you won’t see the bug.