I know this is old, but I am posting this for others that might run across this issue.
Another solution to this would be to AllowAutoRedirect to false on the Request object. If you are programmatically submitting the form, then you probably don't care nor want to be redirected anyway:
HttpWebRequest request = (HttpWebRequest) WebRequest.Create( input.FormCaptureUrl );
request.AllowAutoRedirect = false;