screen was locked...but not?

[btownguy]

I had my Mac screen locked (OSX 10.6.5) the other day. I moved my mouse to wake the screen up and the unlock authentication dialog popped up as expected, but you could see my desktop behind it. Huh? Then I moved the mouse around and I could open up programs and navigate around. My computer was supposed to be locked. WTF?

 

[angelwatt]

There's a setting for how long it takes for the screen to really lock after the screen goes to sleep or to screen saver. You may have caught it at a border case. Is it something that has happened more than once?