Alternate implementation of WriteToStreamAsync

net40.cs

public override Task WriteToStreamAsync(Type type, object value, 
                                        Stream stream, 
                                        HttpContent content, 
                                        TransportContext transportContext)
{                                     
    if (string.IsNullOrEmpty(JsonpCallbackFunction))
        return base.WriteToStreamAsync(type, value, stream, content, transportContext);

    StreamWriter writer = null;

    try
    {
        writer = new StreamWriter(stream);
        writer.Write(JsonpCallbackFunction + "(");
        writer.Flush();
    }
    catch(Exception ex)
    {
        try
        {
            if (writer != null)
                writer.Dispose();
        }
        catch { }

        var tcs = new TaskCompletionSource<object>();
        tcs.SetException(ex);
        return tcs.Task;
    }

    return base.WriteToStreamAsync(type, value, stream, content, transportContext)
               .ContinueWith(innerTask =>
               {
                   if (innerTask.Status == TaskStatus.RanToCompletion)
                   {
                       writer.Write(")");
                       writer.Flush();
                   }
                   return innerTask;
               }, TaskContinuationOptions.RunSynchronously)
               .Unwrap()
               .ContinueWith(innerTask =>
               {
                   writer.Dispose();
                   return innerTask;
               }, TaskContinuationOptions.RunSynchronously)
               .Unwrap();
}

net45.cs

public override async Task WriteToStreamAsync(Type type, object value, 
                                              Stream stream, 
                                              HttpContent content, 
                                              TransportContext transportContext)
{                                     
    if (string.IsNullOrEmpty(JsonpCallbackFunction))
    {
        await base.WriteToStreamAsync(type, value, stream, content, transportContext);
        return;
    }

    using (var writer = new StreamWriter(stream))
    {
        writer.Write(JsonpCallbackFunction + "(");
        writer.Flush();

        await base.WriteToStreamAsync(type, value, stream, content, transportContext);

        writer.Write(")");
        writer.Flush();
    }
}

Brad, in the .NET 4.0 code what's the reason for the two ContinueWith() blocks on the bottom breaking up the write and close operation especially since the code in those async operations is marked as executeSynchronous.