by vector40 » 28 Sep 2005 13:17
Deadbolts are locked in that way, and so are most modern knob latches, using an extra piece (the small, D-shaped piece on one side of the latch) that is pressed in when the door's closed and prevents the latch from moving without the knob turning.
It's true that not all knobs are deadlatched, and some deadlatches just don't work due to shoddy installation (the door and frame are far enough apart that it isn't depressed enough, or the deadlatch is falling into the strike) or malfunctioning design.