Assuming it's a latex-based paint, or something like that, I really don't know.. I think that has something to do with it. It's almost like the walls are too plasticy. But either way it's good you washed that off ASAP. Sharpies a bitch to paint over on account of the fact that it continuously bleeds through. If you don't believe me, check my damages fee from living in a dorm last year. Whoooooops.