Other thing to note is that I have noticed a slightly weird rattle in that same front passenger door when I closed it. Didn't really think much of it at the time.
I took the panel off, and found that the rod going up to the door lock assembly had popped off. This was causing the rattle I heard, and more then likely was impeding the button from locking at random times.
I guess I would have figured this out if I ever would have unlocked the door from the passenger side, but I don't think I've done that for years....hahaha
