Delay operator doesn't work in WPF

[Boredbone]

Delay operator doesn't work under WpfDispatcherTimerProvider.

I think, self.timer.InvokeOnce(self.dueTime - elapsed); is called in Delay<T>._Delay.DrainMessages, but after that, timer.Stop(); is called in WpfDispatcherTimerProviderTimer.Timer_Tick, so it may be unintended behavior.

public partial class App : Application
{
    protected override void OnStartup(StartupEventArgs e)
    {
        WpfProviderInitializer.SetDefaultObservableSystem(ex => { });
    }
    protected override void OnActivated(EventArgs e)
    {
        base.OnActivated(e);

        Observable.Return(Unit.Default)
            .Delay(TimeSpan.FromSeconds(1), TimeProvider.System)
            .Subscribe(_ => Debug.WriteLine("This works fine"));

        Observable.Return(Unit.Default)
            .Delay(TimeSpan.FromSeconds(1))
            .Subscribe(_ => Debug.WriteLine("but here is not reached"));
    }
}