Steps to reproduce this issue:
- Go to this page in edit mode with LivePrevew enabled.
- Click on 'Show preview', wait for the AJAX request to load.
- Scroll down to 'Templates used on this page' below the edit area: it shows multiple times the same list and the next section (hidden categories) is empty.
Reason:
https://git.wikimedia.org/blob/mediawiki%2Fcore.git/HEAD/resources%2Fsrc%2Fmediawiki.action%2Fmediawiki.action.edit.preview.js#L138
There are at least three elements using the 'mw-editfooter-list' class: the template list, the hidden categories used on the page, and the parser profiling data section.