Last modified: 2012-04-19 21:22:12 UTC
The feature was added per bug 24212. However it unconditionally inserts a <link> tag, even if that message/page does not exist on the foreign wiki.
Raising importance as this will save a cross-domain http request on all File-pages when the page doesn't exist (every page view of a File-page of a foreign file)
Server side check and cache the result?
Note that this bug only occurs on the local wiki, not on the 'file sharing repository' itself. So the wikis using another wiki as repository unconditionally include a <link> tag to foreign.wiki/MedaWiki:Filepage.css?action=raw. eg. if MedaWiki:Filepage.css would not exist on Commons, it would not be loaded on Commons' File-pages, but on every en.wikipedia.org view of a commons-file it would be loaded.
Fixed by r91031.