Last modified: 2013-11-22 00:14:05 UTC
Redirection of thumb.php was introduced in I40350121cf. It is plainly broken for MediaWiki installations lacking a 404 thumb handler, since it redirects from thumb.php (which is meant to render the image) directly to the nonexistent thumbnail URL. Even for installations that do have a 404 handler, it is presumably unexpected that thumb.php could redirect to something other than thumb.php. It seems to be an unintended consequence of sharing code with the 404 handler.
Change 96920 had a related patch set uploaded by Gergő Tisza: WIP Make thumb.php redirects point to thumb.php https://gerrit.wikimedia.org/r/96920
