I've managed to implement a Task in my class that downloads a file from my webspace using normal HTTP. That is how I do it:

public async Task DownloadPackageTaskAsync(IProgress<int> progress) 
    {
        var webRequest = WebRequest.Create(new Uri("http://ift.tt/1Cx3LkH"));
        using (var webResponse = webRequest.GetResponse())
        {
            var buffer = new byte[1024];
            FileStream fileStream = File.Create("Path"));
            using (Stream input = webResponse.GetResponseStream())
            {
                if (input == null) throw new Exception("Error while getting the input.");
                int received = 0;
                double total = 0d;
                var size = GetFileSize(new Uri("...")); // Gets the content length with a request as the Stream.Length-property throws an NotSupportedException
                if (size != null) total = (long) size.Value;

                int size = input.Read(buffer, 0, buffer.Length);
                while (size > 0)
                {
                    fileStream.Write(buffer, 0, size);
                    received += size;
                    progress.Report((received/total)*100));
                    size = input.Read(buffer, 0, buffer.Length);
                }
            }
        }
    }

This works well, the file is being downloaded and also if I add Debug.Print((received/total)*100) it outputs the correct percentage, everything is alright. The method is marked as async so that it can be awaited/wrapped asynchronously in a task. The problem occurs in another class that calls the method like that:

var downloadDialog = new UpdateDownloadDialog
            {
                LanguageName = _updateManager.LanguageCulture.Name,
                PackagesCount = _updateManager.PackageConfigurations.Count()
            };

            _context.Post(downloadDialog.ShowModalDialog, null);

                var progressIndicator = new Progress<int>();
                progressIndicator.ProgressChanged += (sender, value) =>
                    downloadDialog.Progress = value;
                _updateManager.DownloadPackageTaskAsync(progressIndicator);

It never calls the anonymous method there that should be invoked as soon as the progress changes, but nothing happens, I debugged it with breakpoints. Maybe I'm using the async-await-pattern wrong (again), I don't really know. Consecutively the UI does not update the progressbar it contains (which it does in the setter of the Progress-property that is initialized above).

I've read different articles but I did not find something that helped me. Help is appreciated.