We have a dealer special based upon the Sterling 520 which arrived from the factory in Nov 2005 with their new plastic formed bed and locker bases. All the overhead locker hinges were tighened twice by the dealer to solve this issue, but that did not work, especially for the larger airliner type doors.
The manufacturers were contacted and they, probably reluctantly, agreed to the fitment of a THIRD hinge, which has certainly solved the problem for us.These things do hurt when they suddenly smack you.
Might be worth approaching your supplying dealer for them to try this for you.