Results.txt

SyncCtx/IsThreadPool/ThreadId: System.Windows.Threading.DispatcherSynchronizationContext/False/8
SyncCtx/IsThreadPool/ThreadId: System.Windows.Threading.DispatcherSynchronizationContext/True/10

ResultsInNet45.txt

SyncCtx/IsThreadPool/ThreadId: System.Windows.Threading.DispatcherSynchronizationContext/False/8
SyncCtx/IsThreadPool/ThreadId: /True/11

Window1.cs

using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
using System.Windows;

namespace WpfApplication3
{
    public partial class MainWindow
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private async void ButtonBase_OnClick(object sender, RoutedEventArgs e)
        {
            Debug.WriteLine("SyncCtx/IsThreadPool/ThreadId: {0}/{1}/{2}", SynchronizationContext.Current, Thread.CurrentThread.IsThreadPoolThread,
                Thread.CurrentThread.ManagedThreadId);

            await TaskEx.Run(() => Thread.Sleep(1000)).ConfigureAwait(false);

            Debug.WriteLine("SyncCtx/IsThreadPool/ThreadId: {0}/{1}/{2}", SynchronizationContext.Current, Thread.CurrentThread.IsThreadPoolThread,
                Thread.CurrentThread.ManagedThreadId);
        }
    }
}

Window1.xaml

<Window x:Class="WpfApplication3.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Button Click="ButtonBase_OnClick" Content="Do Stuff" />
    </Grid>
</Window>