It's quite possible that the script you are submitting to on that server is returning a redirect to you. That's very common with login screens since they usually give you a cookie before you go to the next page so that you're logged-in status will be noted. Try checking for a cookie (just out of curiosity mainly :) from that response:

  my $header = $response->header('Cookie');
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Make sure that you have redirects turned on for mech, so that your agent will automatically follow the redirect. See the redirect_ok() method.

If mech won't automatically follow a meta refresh redirect, then you could try parsing the response with something like HTML::Parser, then just submit to the new url (and make sure you use the same agent with a cookie_jar if you were given a cookie from the previous submition). HTH