1) Visit https://www.mediawiki.org/wiki/Special:NewMessages
2) Click a "mark as read" button
I. Observed: the button itself and the link to the thread disappear, but the thread next to them doesn't.
II. Expected: the thread disappears and I can read the next one in the same position.
III. Observed and expected: the read thread is not listed.
Currently under discussion at https://commons.wikimedia.org/wiki/MediaWiki_talk:Gadget-HotCat.js#Errors_in_webconsole_-_deprecated