Fiddler trace (ZIP archive with a funny name)

Your extension seems to give some rather odd HTTP responses. Namely:

HTTP/1.1 200 OK
Server: Apache
X-Powered-By: PHP/5.3.10-1ubuntu3.9+wmf1
X-Content-Type-Options: nosniff
Cache-control: private
MediaWiki-API-Error: unknownerror
X-Frame-Options: DENY
Vary: Accept-Encoding
X-Vary-Options: Accept-Encoding;list-contains=gzip
Content-Type: text/xml; charset=utf-8
X-Varnish: 675837389, 1807899246
Via: 1.1 varnish, 1.1 varnish
Content-Length: 129
Accept-Ranges: bytes
Date: Fri, 21 Feb 2014 05:16:39 GMT
Age: 0
Connection: keep-alive
X-Cache: cp1053 miss (0), cp1055 frontend miss (0)

<?xml version="1.0"?><api servedby="mw1135"><error code="unknownerror" info="Unknown error: &quot;tpt-target-page&quot;" /></api>

This was for an attempt to save "MediaWiki 1.21/wmf5/el" on www.mediawiki.org.

(Raw request/response pair attached in Fiddler's ZIP-based format; would be easiest to open in Fiddler, but anything else that understands raw HTTP request/response pairs should be able to make sense of the data.)

I'm assuming it's from this extension because it only happens on pages that, when edited from normal UI, open in your fancy translation tool.

I have two questions:

1. Why is this a "200 OK"? Things are clearly not OK; it should probably be a 500, or possibly a 403.

2. Why is the error so non-specific?

Version: unspecified
Severity: normal

Attached: