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Using a WPF UI stream should always provide STA flat mode, right?

In my WPF application, I communicate asynchronously with the server. The callback will therefore not be executed in the user interface thread, and since I need to do some WPF stuff there (create an InkPresenter object), I need it to run in the user interface thread. Well, actually the requirement is that it starts in a thread with STA apartment mode. I tried to create a new thread with STA mode, but the result was that the UI thread could not access InkPresenter because it was "the owner of another thread."

In the callback, I want to use a dispatcher to call my function requiring an STA. Does this sound like the right approach? I am doing it now, but still fail. In my callback function, I run the following function, which now tries to verify that the address function is running in the user interface thread.

private void UpdateAnnotationsForCurrentFrameCollection()
{
    if (Dispatcher.CurrentDispatcher.CheckAccess())
    {
        DoSomethingIncludingInkPresenter();
    }
    else
    {
        Dispatcher.CurrentDispatcher.Invoke(DispatcherPriority.Normal,
           new Action(DoSomethingIncludingInkPresenter));
    }
}

private void DoSomethingIncludingInkPresenter()
{
    var inkPresenter = XamlReader.Parse(_someXamlString) as InkPresenter;
    // Do something with the inkPresenter.. 
}

As the example shows, I use CheckAccess () to make sure that I only call the function if it is not already running in the user interface thread. When my callback calls this function, CheckAccess () is always right, but Dispatcher.CurrentDispatcher.Thread.ApartmentStateit is MTA. What for? I tried to remove CheckAccess () and always do Invoke, but ApartmentState remains MTA, and the creation of InkPresenter fails.

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CheckAccess CurrentDispatche, :
 someControl.Dispatcher.CheckAccess

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private void SomeMethod(Dispatcher dispatcher)
{
  DoOtherThingsThatCanDoMTA();

  dispatcher.Invoke(new Action(()=>
  {
    DoSomethingThatRequiresSTA();
  }));
}

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