Recently, the Minecraft username filter has been catching words that aren't actually offensive as offensive, because they happen to have offensive words in them. (i.e. Cl'ass', 'Ass'ociation, Gl'ass') All these words technically have swears in them, but aren't offensive in any way.

My own username, Rassy, was hit with this issue, and because of it I've lost username priority and the ability to get it back.