THE VAN WAS PULLED IN TO A DRIVEWAY WITH A SLIGHT TILT, PUT IN PARK, WITH THE KEY REMOVED FROM THE IGNITION, IN PARK. THE PRIMARY DRIVER ALMOST ALWAYS USES THE PARKING BRAKE, AND BELIEVES IT WAS ON AT THIS TIME. THE SLIDING DOOR BEHIND THE DRIVERS SIDE DOOR WAS OPENED, SOMETHING TAKEN OUT, AND CLOSED. AT THAT POINT IN TIME, THE VAN STARTED ROLLING BACKWARD, TO THE POINT WHERE IT ACTUALLY IMPACTED THE HOUSE ON THE OTHER SIDE OF THE STREET. PROBLEM HAS NOT BEEN REPRODUCIBLE. TAKEN TO THE DEALERSHIP, THEY PERFORMED BASIC TESTING, COULD NOT REPRODUCE THE PROBLEM, BUT WILL NOT STATE THAT THE CAR IS SAFE AT THIS POINT IN TIME.