T31 Rear Door will open from outside when car is locked.

[X-Man]

My rear passenger door will open from the outside when the car is locked.  I can lock myself in using the key fob and tried all positions on child lock. New lock fitted by garage who then said it was a wiring fault in the door pillar and it worked for a brief period.  now back to square one.

During all this time the lock has actuated and disabled the internal handle when locking but not the external.

I'm baffled!