Grouped Recent Changes/Watchlist displays a pair of square brackets around expand arrows since today.
Steps to reproduce:
- Go to https://www.mediawiki.org/wiki/Special:RecentChanges
- In the options at the right, above "List of abbreviations", click and tick "Group results by page"
- Grouped changes on a page should display an arrow (this was working yesterday)
- Grouped changes on a page display an arrow surrounded by square brackets