there is a spring in one of the handles of the door. its prob the drivers door. . . when it comes off or is broken, sometimes it causes it to do that. when you lock the drivers door, it will lock the unlock both doors.
the problem you have now is the begining phase i guess you could say, its what happen to my teg. after it becomes hard, it will break. then once you get it locked, you can not open it. you have to dismantle the handle and find the broken spring, then put it back together. it is not easy or fun.....

i would take it to a shop, and get them to fix it. OR pay 50-75 bucks for a new door with a key and just have two keys for your teg.