I wasn't sure where to report this bug, but when editing multiple posts via the bulk option, I have posts that have a category already defined, but I want to redefine it to be a different one. So the initial category is 'events', and I want to change it to be just, 'archives'. I select the couple of posts to change, go to the buld-edit option, and select only 'archives' and click submit. When the posts come back up, they now have both 'archives' & 'events'. So I'm not sure if this is the intent and I have to individually change only to 'add' categories, or if it works when removing them as well.