Passat b5.5 central locking issue

[Quavers]

Our 04 plate passat tdi has a problem with the central locking.
Lock with the fob and all doors lock - almost immediately rear o/s door unlocks.
However, if I lock the car from inside using the switch on the drivers door the doors lock and unlock as normal.
I am perplexed.

[annodomini2]

Microswitch in lock mechanism, common fault, replace the lock or repair the switch.

Plenty of stuff on the Web if you Google it