I've seen this mentioned before and I thought it was true but it isn't: the key is not needed to close the cas cap filler door. I was in for my biannual emissions check and I had unlocked and left open the door so the gas cap could be pressure tested. I was watching the tech do the test in the side view mirror and was preparing to offer him the key to enable him to close the door when he just pushed it shut as easy as pie. I tried it later myself and sure enough, it just pushes shut like most normal cars. I have no idea why I never tried this before myself.