title: YesNo MessageBox not closing when x-button clicked
body: <p>When I open a MessageBox with options YesNo, the (usually) cancelling cross in the upper right is shown but has no effect.</p>
  
  <pre><code>System.Windows.MessageBox.Show("Really, really?", "Are you sure?", MessageBoxButton.YesNo);
  </code></pre>
  
  <p>If I offer YesNoCancel as options, clicking the cross closes the Dialog with DialogResult Cancel.</p>
  
  <pre><code>System.Windows.MessageBox.Show("Really, really?", "Are you sure?", MessageBoxButton.YesNoCancel);
  </code></pre>
  
  <p>I would have expected that the cross is "looking disabled" if not hidden at all, when clicking it has no effect.
  Probably I am not the first one observing this.
  What is your favorite way to hide/disable this button or workaround the issue?</p>
  
  <p>Note: I would prefer a solution that does not use System.Windows.Forms, since I am dealing with WPF projects and would like to avoid any InterOp if possible.</p>