The legend for changes is not displayed normal (totally unstyled by js) if a non-existing page is specified.
Diffing the html-output shows that mediawiki.special.changeslist and mediawiki.special.changeslist.enhanced are not requested from resource loader.
Manually executing "mw.load('mediawiki.special.changeslist');" restores the expected design.
Not a big deal. As far as I see it won't normally occur to users unless they manually type in by mistake a page title which doesn't exist.