Action (() => {}) through the dispatcher measures ui

I tried a simple example of asynchronous await with and without .ConfigureAwait(false)

.
With the help .ConfigureAwait(false)

you can update the ui with the dispatcher, which is unchanged. This is case 1 and 3 in the code below - it works and I can figure out how it works.

My question is about case 2, where I add - completely unnecessary - update
Action(() => { })

via the dispatcher.
This sometimes freezes my ui. Especially after calling the event handler again.
Can anyone explain why ui freezes in case 2?

private void Test_Click(object sender, RoutedEventArgs e)
{
    Test();
}

public async void Test()
{
    Print("Start task");

    // Case 1 & 2
    await Task.Delay(2000);
    // Case 3
    await Task.Delay(2000).ConfigureAwait(false);

    Print("Finished task");
}

void Print(string text)
{
    // Case 1 & 2
    Output.Inlines.Add(new Run(text) { Foreground = Brushes.Blue, FontWeight = FontWeights.Bold });
    // Case 2 only
    Output.Dispatcher.Invoke(System.Windows.Threading.DispatcherPriority.Background, new Action(() => { }));

    // Case 3
    Output.Dispatcher.Invoke(System.Windows.Threading.DispatcherPriority.Background, 
       new Action(() => 
       {  
         Output.Inlines.Add(new Run(text) { Foreground = Brushes.Blue, FontWeight = FontWeights.Bold 
       }); }));
}