Hhhippo reports at https://www.mediawiki.org/wiki/Topic:S5xg30ypdeuaov32
"On my watchlist (with both tog-usenewrc and tog-extendwatchlist enabled), I see today's edits to Talk:Sandbox by Nirmos and EBernhardson both listed as belonging to topic [[User:Nirmos]], while in fact EBernhardson edited a different topic.
It's fine with tog-usenewrc disabled, and both edits are shown with tog-extendwatchlist disabled, so they are to some extent recognized as belonging to different "pages".
Update: It's the topic creations, not the comments that behave like this. I'd suggest they should be shown as edits of the board, not of one of the topics.