LW/LZ Door Locking problem

[KosCo]

I have an LW Focus and recently have had a problem with the front passenger door not locking properly. The doors make their locking sound, the rear view mirrors turn in and everything appears to be locked. But recently on 2 occasions I have opened the passenger door and the door has opened but none of the other doors have opened and the rear view mirrors have remained closed. The first time it happened, I though it was just something I had done. Today after it happened, I locked the car again and placed the key fob out of range. I was able to open the passenger door by hand and the door opened and then I tried each of the other doors including the boot and none of these would open. So I am assuming that the front passenger door may not be locking every time. It doesn't happen every time though. Just asking for any help/suggestions. Thanks in advance.