So, my roommate was playing Oblivion on his normal, non-XBL account. He wanted to do something DLC related (like go to the Shivering Isles) but noticed it wasn't marked on the map, nor was any of the other DLC. Thinking that we just hadn't redownloaded the DLC after having got our new Xbox a couple months back, so he got on my account and redownloaded them. However, the fact that each own downloaded instantly hints at the fact that it was already there to begin with. When he went back into the game on his account, no DLC. And we know this is a new thing because previously I had made several different accounts on the old Xbox 360 for the sole purpose of playing Oblivion with different characters because unlike Mass Effect, it doesn't separate save files between characters. You get one date sorted list for all the characters you've made.
Anyway, my roommate then decided to play our Fallout 3: Game of the Year Edition instead thinking that since all the DLC was on a disc already installed on the system he should be able to access this... again, no DLC.
What's wrong and how do I fix it? My roommate would rather he didn't have to start all over again on my account.