that could be due 2 the passenger door lock not being as worn as the drivers side lock,it sounds like sumthing in the catch could b sticking and causing the central locking 2 think that maybe the handle is being held up or the door isnt shut properly,maybe take the catch out of the door and clean it up and soak it in sumthing like wd40 or sum thin spray grease,it could be that the old grease on the catch could b clogging it up a bit when it gets cold