2001 V70 Driver Door Won't Stay Locked
 

I have a 2001 V70 T5 and the driver's door will not stay locked. Doesn't matter how I lock it -- key fob, key in lock, or inside button. I lock the door and it immediately pops back "open."
I read in another forum where someone said if any of the door lock actuators are bad it will automatically unlock the driver's door. He recommended having the Volvo dealer check the system out using VADIS to figure which door lock actuator is causing the problem. Apparently it doesn't have to be the driver's door.
I asked the Volvo service rep about checking the car with VADIS. He said VADIS doesn't test the locking systems. Brought the car to the Volvo dealer 3 weeks ago with another problem (car cranks, but won't start) and asked them to check the door locks. Of course they tell me the door locks are working just fine. They saw no problem.
Any suggestions on how to figure out what the problem might be? I've checked everything I know how and nothing seems to work.