MW 1.25.5, RT 1.1.1, PHP 5.4.45
Then trying to do a replacement in the talk namespace (2) I get the following fatal:
[Thu Jan 07 09:33:32 2016] [error] [client 91.65.247.81] PHP Fatal error: Call to a member function getArticleID() on a non-object in /.../w/extensions/ReplaceText/SpecialReplaceText.php on line 445, referer: http://www.example.org/Special:ReplaceText
Other namespaces including custom namespaces and other talk namespaces work allrighty.