Comportamento estranho usando AsyncCTP

gistfile1.cs

            public async Task<string> DownloadTaskAsync(string url) {
                HeadOnly = true;

  
                bool loop;
                HttpWebResponse responseAsync;

                do {
                    loop = false;
                    var webRequest = (HttpWebRequest) GetWebRequest(new Uri(url));
                    webRequest.AllowAutoRedirect = false;
                    webRequest.KeepAlive = true;
                    responseAsync = (HttpWebResponse) await webRequest.GetResponseAsync(); /* Em um UNICO casos esta linha causa uma saída repentina neste método sem deixa exception qualquer outra coisa, retornando a linha de quem a chamou. */
                    //var responseAsync = (HttpWebResponse)webRequest.GetResponse();
                    //var responseAsync = (HttpWebResponse)GetWebResponse(webRequest);

                    int statusCode = (int) responseAsync.StatusCode;
                    Console.WriteLine(url + " - " + statusCode);
                    if ( /*(new[] { 301, 302 }).Contains(statusCode)*/statusCode == 301 || statusCode == 302) {
                        Console.Write(url);
                        url = new Uri(new Uri(url), responseAsync.Headers["Location"]).ToString();
                        _url = url;
                        Console.WriteLine(" ---> " + url);
                        loop = true;
                    }

                } while (loop);
    

                if (responseAsync.StatusCode == HttpStatusCode.OK && responseAsync.ContentType.StartsWith(@"text/")) {
                    _progress.Id = CrawlHelper.IdPage(url);
                    HeadOnly = false;
                    return await this.DownloadStringTaskAsync(new Uri(url), _cts.Token, _progress);
                }
                return string.Empty;
            }