I think you have a broken wire where the wire bundle comes out the door on
its way to under the dash. When you unlock the door, at the momoent the door
unlocks the circuit interprets the broken wire as you locking the door
again. The wire can be broken inside the insulation, so a visual check will
not do in that case. Time for your VOM(volt ohm meter). I did mine long ago
and I can't remember the wire color to check. The Bentley would give you the
info on that. Many of the wires in my Westy were too short. The drivers door
gets the most use and the constant flexing causes a failure. I spliced in an
extra 12 inches to reduce the tension on all the wires going from the door
to dash. I had problems in both doors and I did not want to revisit each
circuit. My cruise control and rear hatch lock were the same thing.
Good luck!

Bob Wing
89 Westy