Driver's Side Front Door Not Locking

My husband came home today with some interesting news: the driver's side door on our 2005 Prius didn't want to lock. After some discussion and experiementation we came up with this list of symptoms:

• When you push the lock button on the fob, all doors will lock except for the driver's side front door
• When you push the lock button on the console, every door locks except for the driver's side front door
• When you use the manual key (the one inside the fob), if you turn it a little, all the other doors lock. You really have to TURN the key to get it to lock the driver's side door.
• The only way we can lock the door is to manually flip the lock (the little flip switch next to the handle that's on the inside of the door) and then close the door.

NOTE - The car does not have smart-key installed.

Our biggest questions are: 1) what the heck is wrong with this door? (possession maybe? ;-) ) and 2) is it still covered under our warrentee?

Thanks in advance...
Anne