"enhanced watchlist" requires usenewrc I assume?
Public testcase welcome, if possible...

(In reply to comment #1)

"enhanced watchlist" requires usenewrc I assume?

Correct. Enhanced Special:RecentChanges shows the same regression

Public testcase welcome, if possible...

A testcase needs an account with preferences set:

https://commons.wikimedia.org/w/index.php?title=Special:Preferences&success=1#mw-prefsection-rc
"Group changes by page in recent changes and watchlist (requires JavaScript)"

AND

https://commons.wikimedia.org/w/index.php?title=Special:Preferences&success=1#mw-prefsection-watchlist
"Expand watchlist to show all changes, not just the most recent"

I am not aware of any URL parameter to simulate these settings without an account.

Looks okay on https://commons.wikimedia.org/wiki/Special:RecentChanges?enhanced=1 for IE8

One possible change to the enhanced changelist which can break this, is gerrit 39759. Have you clear you cache, to get the newest stylesheets? (ResourceLoader should do that automatically, but maybe it was not done)

Thanks Umherirrender. Cache clearing fixed the issue #grmbl