Here's the capture from the FF plugin Live HTTP headers, as you can see it's the same Location: redirect as when I post /somesite/login directly to the "backend".

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http://192.168.1.100/somesite/login
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POST /somesite/login HTTP/1.1
Host: 192.168.1.100
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.15) Gecko/2009102815 Ubuntu/9.04 (jaunty) Firefox/3.0.15
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
Referer: http://192.168.1.100/somesite/login
Cookie: trac_form_token=8a237ed09a65182989b124f6; trac_session=f3274da16804f3b8fbc786ea; somesite_ZA_=6943021B818EE459F689B7CB2F203A8A3F0AD05F
Content-Type: application/x-www-form-urlencoded
Content-Length: 127
__FORM_TOKEN=8a237ed09a65182989b124f6&referer=http%3A%2F%2F192.168.1.100%2Fsomesite&user=user&password=pass
---
---

HTTP/1.x 303 See Other
Server: nginx/0.7.65
Date: Thu, 04 Feb 2010 06:24:20 GMT
Content-Type: text/plain
Connection: keep-alive
Location: http://dev.somesite.co.za:8001/somesite
Content-Length: 0
Pragma: no-cache
Cache-Control: no-cache
Expires: Fri, 01 Jan 1999 00:00:00 GMT
Set-Cookie: trac_auth=21e23f09d99de1381683a341118d37ad; Path=/somesite
Set-Cookie: trac_session=f3274da16804f3b8fbc786ea; expires=Thu, 04-Feb-2010 06:24:35 GMT; Path=/somesite
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