Board Thread:General Discussion/@comment-24751639-20160620015459/@comment-26037236-20160620015802

You need to edit using the source editor. You can't remove categories using the add categories section at the bottom of the page. You will need to remove the [Category:CATEGORYNAME] from there. It won't look like it works immediately after either, due to a bug. Remove it, and come back after a few hours to make sure it worked correctly.