There was MediaWiki:Recentchanges-summary message added recently. However, there is already MediaWiki:Recentchangestext.
When MediaWiki:Recentchangestext uses certain CSS (negative margins e.g.) to position elements, MediaWiki:Recentchanges-summary breaks it.
The solution would be to empty the MediaWiki:Recentchanges-summary message, but neither "-" nor empty page works. The first case shows the "-" character on Special:RecentChanges, the second shows the default message. So it is currently impossible to get rid of that message at all.
For the time being before fixing, this should be removed from live WMF wikis, as it breaks many Special:RecentChanges pages.
Version: unspecified
Severity: major