I think there are two different systems at work here. One is the mechanism that allow the door to open and close when you press on it (like some cabinet doors do). The locking system, which is tied to the door locks (if you lock the car, there is a delay on the fuel door being locked), simply keeps you from opening the door. If your fuel door won't close at all, I don't think it's the locking system, unless it's actually in the locked position somehow and preventing the door from closing, but according to the manual "if the fuel-filler flap is closed after locking the doors, the fuel-filler flap cannot be locked". Doesn't say it cannot be closed, so I think it's the latch part at fault, not the lock.