Mechanize users - Dec 2011 - Mechanize GETting twice without redirect?

[Cross posted to Ruby on Rails Forum and Mechanize mailing list.]

I''m using Mechanize for page scraping (Ruby 1.9.2 / Rails 3.0.5 /
Mechanize 2.0.1).  I''m seeing a case where a single

  agent.get(url)

generates two HTTP GETs.  Why is this happening?

The response to the first GET is a 200 (no redirect) and doesn''t have
any meta-refresh.  I don''t see why Mechanize is issuing the second GET
(which happens to be failing with an EOFError with Content-Length /
body length mismatch).

Details: I''m using the nifty Charles web proxy debugger to monitor
browser / server interactions.

====In the original browser + server exchange, I see:

Req: POST /login/Login HTTP/1.1
Rsp: sets two cookies + HTTP/1.1 302 Moved Temporarily =>
        https://online.nationalgridus.com/eservice_enu/

Req: GET /eservice_enu/ HTTP/1.1
Rsp: set a cookie + HTTP/1.1 200 OK
The body contains onLoad Javascript to set this.location
''start.swe?SWECmd=Start''

Req: GET /eservice_enu/start.swe?SWECmd=Start HTTP/1.1
Rsp: sets four cookies + HTTP/1.1 200 OK

====In the mechanize = server exchange:

My code: page2 = agent.submit(login_form)
Req: POST /login/Login HTTP/1.1
Rsp: set two cookies + HTTP/1.1 302 Moved Temporarily =>
        https://online.nationalgridus.com/eservice_enu/

Req: GET /eservice_enu/ HTTP/1.1
Rsp: set a cookie + HTTP/1.1 200 OK
The body contains onLoad Javascript to set this.location
''start.swe?SWECmd=Start'', but Mechanize can''t follow
that
automatically.  So I do an agent.get() to emulate it:

My code:   page3
agent.get("https://online.nationalgridus.com/eservice_enu/start.swe?SWECmd=Start")
Req: GET /eservice_enu/start.swe?SWECmd=Start HTTP/1.1
Rsp: sets four cookies + HTTP/1.1 200 OK

Note that at this point both the user driven and mechanize driven
interactions appear to be identical.  But Mechanize appears to
generate another GET all by itself:

Req: GET /eservice_enu/start.swe?SWECmd=Start HTTP/1.1
Rsp: sets four cookies + HTTP/1.1 200 OK

... and this response throws an EOFError:
Content-Length (536) does not match response body length (524) - EOFError

====So: Why did Mechanize generate that last GET without me asking it to?
 Was the EOFError actually in the first GET and it''s doing a retry?
If so, how do I work around the length mismatch?