Correctly receiving data using StreamSocket hangs

I am using a StreamSocketListener to receive data on a Windows Phone 8 (acting as server) sent by a HTTP POST client. I can receive the data but when all data is read the DataReader.LoadAsync() method hangs until I manually cancel the connection from the client:

_streamSocket = new StreamSocketListener();
_streamSocket.ConnectionReceived += _streamSocket_ConnectionReceived;
await _streamSocket.BindServiceNameAsync("30000");


private async void _streamSocket_ConnectionReceived(StreamSocketListener sender,
        StreamSocketListenerConnectionReceivedEventArgs args)
{
    using (IInputStream inStream = args.Socket.InputStream)
    {
        DataReader reader = new DataReader(inStream);
        reader.InputStreamOptions = InputStreamOptions.Partial;

        do
        {
            numReadBytes = await reader.LoadAsync(1 << 20);  // "Hangs" when all data is read until the client cancels the connection, e.g. numReadBytes == 0
            System.Diagnostics.Debug.WriteLine("Read: " + numReadBytes);

            // Process data
            if (numReadBytes > 0)
            {
                byte[] tmpBuf = new byte[numReadBytes];
                reader.ReadBytes(tmpBuf);
            }
        } while (numReadBytes > 0);
    }

    System.Diagnostics.Debug.WriteLine("Finished reading");
}

What's wrong with this sample code?