Sounds like the passenger door mechanism is sticking. This is a reply i gave someone else on the same subject
I had exactly this problem on my Tipo. The problem was that the passenger door lock mechanism was sticking. When i locked the passenger door from the outside, the central locking worked fine, as i was able to apply enough pressure to overcome the 'stickiness'. When i locked the central locking from the drivers side, it locked, and then immediately popped up again. I am sure this is because the central locking mechanism in the passenger side didn't have enough oommpphh to overcome the stickiness (whereas the key did manage it). Took me a while to suss that the problem was actually in the passenger side, as the problem only occurred when the drivers side mechanism was used. If the problem occurs when using the key on both driver and passenger side, the problem may lay in the rear doors.
Hope that helps somewhat. Regards Neal