I can relate to that Evan. Nobody was ever able to give me a sensible answer as to why I should have to show the working as long as the answer was right. They used to argue that if I didn't show the working they would not be able to find out where I went wrong. I told them that didn't matter because if I got it wrong I would make sure I found out what I did wrong.
Interestingly, they only ever seemed to take the matter up when the answers were all right, never on the rare occasion when one was wrong.