Check the Wiring in the rubber tube between door and body, ( use a hook and give them all a gentle tug ) and if you can't find a broken wire, Check the other side rear just for the hell of it. For some reason, the nearside is very common for breaking, I suppose its the side that gets most use for passengers to exit onto the causeway.

It is weird that you can here the door lock and unlock and it still stays locked but its just another thing that you can't take for granted on modern cars, With old cars if it went clunk clunk and didn't lock or unlock, you knew the latch assembly was faulty.

And Yes, The wiring in the N/S/R door can affect the other doors. ( Not sussed out why yet though ) But I suppose some clever guy will come along and tell us why.