have you checked to see if the drivers door lock (button thing inside car) goes ALL the way up when you unlock the door? i know several cars that, if the lock isn't ALL the way up, as a sort of security device, it will lock when the handle is pulled. This is for those times when someone doesn't push the lock ALL the way down when they lock it, so the door is still locked, kinda thing... understand? Hard to explain i guess, i tried!
Az