There are two little arms that engage with the springloaded wind deflector at each side of the sunroof. As the sunroof closes, these arms get pushed down, thus pulling down the deflector. On one of my 740 cars the pin that engages the arm with the deflector came out, and I ended up with the same problem. Turned out that the slot in the arm had rusted out because I wasn't paying attention. I was able to fix it with epoxy and a small strip of aluminum fairly neatly.