Wikimedia Bugzilla is closed!

Log in to a wiki, visit a Flow board and create a post containing the wikitext
  [[File:Şirince_(doyler79).jpg|thumb]]

when you edit the wiki text, note it has become
  [[File:Şirince_(doyler79).jpg|thumb|link=File:%C5%9Eirince_(doyler79).jpg]]

It only happens if the file name has an accented character. This sounds like an edge case of bug 49844, which was fixed.  If I run the wikitext on line 2 through the round-trip parser http://parsoid.wmflabs.org/_rtform/ , the link parameter doesn't appear.  It's in the HTML generated by http://parsoid.wmflabs.org/_wikitext/ , as a data-parsoid parameter:
   <figure ... data-parsoid='{"optList":[{... ,{"ck":"link","ak":"link=File:%C5%9Eirince_(doyler79).jpg"}], ...] }

I don't think that percent encoding is needed, the link should only be URL-encoded when put in a URL. For what it's worth the wikitext from Parsoid doesn't work if you copy it to a regular page, "link=File:%C5%9Eirince_(doyler79).jpg" appears as the caption.