91 300TE 4matic (Gretel):

We rarely lock the doors (not much need 'round here), but when we've needed to, locking the driver's door locks all doors (including rear hatch) just fine. Unlocking the driver's door unlocks all doors just fine.

If the wagon gets parked, unlocked, and all doors closed - and then you open and close the driver's side (left) rear door, all doors lock. Happens every time with that door, never happens with any other doors.

Any clue where I should start looking to find the root cause?

__________________
1961 220b: first project car - sold.
2000 CLK 430: first modern Benz - sold.
2001 CLK 55: OMG the torque!!! - sold
1972 280SE 4.5: Baby Gustav
1991 300TE 4Matic: Gretel the Snow Bunny - sold
1978 300SD: Katz the Free Man - given away
1980 Redhead: Darling Wife