I think the problem lies with the keyless entry control circuit. The motor will not start without getting electricity and none of the position switches or the dash operating switch are energized when the car is shut off so they cannot do anything to energize the motor.
The car's electrically operated mechanisms may have some kind of position switches that tell the control system that you access with your remote key the status of items like the windows and the roof so when you ask the system to shut the roof and windows when it locks the vehicle it "knows" what to do. I think the tilting sunroof does have some limit switches to sense position, which could either be out of adjustment (telling the system it is not in the proper position when you lock the car) or the system could be influenced by interference. There could be electromagnetic interference from some adjacent source, or, since I believe these things work with an infrared signals as well, you could be getting interference from some other infrared controlled item in your home, like a tv or stereo remote, or possibly a neighbor's stereo remote.
I would not suspect the motor or the dashboard control switch as they need some other help to support clandestine operations. If you are locking the car from a distance with the remote feature on the key maybe the sunroof moves at that time and you do not see it from where you are standing?
You should move the car to another place and see if it continues to happen. Fixing these systems can be costly and frustrating. Good Luck, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)