I think the reason is because there is no "K2KLabel" op defined in [k-prelude.maude](https://github.com/kframework/k/blob/master/lib/maude/lib/k-prelude.maude). Would it make better sense to add that to the maude file instead of filtering it out here? Also, I was thinking that this wouldn't affect the Java backend -- mostly because of the directory structure, I guess (this being in "backend/maude").