It's working exactly as intended, I'm afraid. Why should the image of A put onto B, carry over if you try to glamour B to C? I don't think it's a transitive process, which is why we're at least lucky A isn't destroyed when we use a glamour prism to put A's appearance onto B. It's still perfectly good to make a glamour of A onto C, with the addtion of a new glamour prism.