Recently I've spotted several cases where all categories of a page were added to it a second time.
Aside from an anonymous contribution I can only remember your edit. Do you still know how you edited that page (visual editor vs. classic editor, (non)-source mode, section-edit)? I suspect this to be another bug.
Edit: From the edit-summary I already see that it must have been section-edits...
I'm not quiet sure, anonymous editors also use the Visual Editor by default and classic-editor section edits are only available if you know how to manipulate the URL. However it might be that they get an summary prompt by default. I can't test it right now since the visual editor doesn't load correctly for me at the moment.
Anyway, when it get's fixed I'll see it in the technical updates, so I'd say if the problem still persists afterwards, we can create a new report for it.