Yeah, the corraline isn't easy. But if anything will touch it(like which mine doesn't a ton anymore on the rocks), it will be an urchin. And neither of mine get on the back glass that often.
Mine does more if the tiny bit of diatom that may every once in a blue moon show up.. The long spine has ate corraline, but I think, like you said, that it's so thick and so much, that I don't notice much anymore.. Corraline is a blessing and a curse. It's very good for letting you know if something happens, as it will bleach first, but for its growth on glass, yeah, lol, it does become a nuisance.. The rose corraline is even worse though, and I will never, ever put that in a tank again on purpose..