The spring might be getting old and worn out. I remember a few times when I was locking my car the locking pin for the gas door hit the tab inside at the right angle and the door popped completely open. I've had to replace that spring 3 times now.
1999 Techno Violet Metallic BMW M3
2005 Audi B6 S4 quattro 6MT
2004 BMW 330i
1986 BMW 535i