Why does this code stop?

[MrNorth]

private async Task<string> Post(string url, string postdata)
        {
            var request = WebRequest.Create(new Uri(url)) as HttpWebRequest;
            request.Method = "POST";
            request.ContentType = "message/rfc822";

            byte[] data = Encoding.UTF8.GetBytes(postdata);
            request.ContentLength = data.Length;

            using (var requestStream = await Task<Stream>.Factory.FromAsync(request.BeginGetRequestStream, request.EndGetRequestStream, request))
            {
                await requestStream.WriteAsync(data, 0, data.Length);
            }

            WebResponse responseObject = await Task<WebResponse>.Factory.FromAsync(request.BeginGetResponse, request.EndGetResponse, request);
            var responseStream = responseObject.GetResponseStream();
            var sr = new StreamReader(responseStream);
            string received = await sr.ReadToEndAsync();

            return received;
        }

The above code halts at the using statement. The method is called from a windows phone 8 Project, where I know they run async methods on the UI thread. But surely isn't async/wait the way to handle this?
What I want is this request-response to fnish, then continue to execute the UI thread. Not to block it completly like this code does.

Is the code wrong? Do I call it wrong?

string x = Post(url, data).Result;
           return x;

To be honest Im not 100% comfortable using the new syntax, and the "feature" windows phone 8 has to run async threads on UI thread, I dont like at all. It is somewhat strange, that if I ´do this as I use to with callbacks and stuff, the UI thread will continue execute while the code in the async method executes (as it should) but when I use an AutoResetEvent.WaitOne() I block Everything, even the async method.

confused.....
/S