Car door lock jammed, can't unlock from the outside?

I have a Ford Fiesta mk4 with a frustrating door lock problem. Its door lock can be locked from the outside, but not unlocked. If the door closes, most of the time it seems to just lock itself. Every time I get in the car I have to unlock the passenger side door, reach over and open the driver's side door, walk around and get in. The car has no central locking system or anything like that if it's any help.

Thanks in advance for any advice!

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