meta.discourse.org/search.php is routed to a particular route in the application, but that route doesn’t know how to respond to a .php format. This results in a ‘406 - Unacceptable’ response, which Discourse doesn’t really know how to handle.
meta.discourse.org/wark.php is not a route in the application, so it’s dropped by the router and returns a 404 - Not Found response, which Discourse knows how to handle.
This could be solved by routing 406 responses to the 404 landing page