In the 2017 wikitext editor, after I
- make an edit
- watch the preview
- go back to edit
the number of the plus (+) icons in the bottom of the page, which are after the categories will be more every time when I do the previous ones. The problem is that it can easily increase size of the editing-tab if you are editing a page with a lot of category (and you make lots edits). Here you can see a video about the bug.