If I click "Reply" at (for example) https://www.mediawiki.org/w/index.php?title=Topic:Sn3mt38amyu5b5xj&topic_showPostId=sno5utzbrd7u6e2c#flow-post-sno5utzbrd7u6e2c
then it opens multiple edit-areas.
Confirmed in Firefox and Chromium, logged-in and -out, on Ubuntu.