title: Viewport3D disable rescaling / resizing
body: <p>How can I disable the following strange resize / rescaling behaviour of a Viewport3d in WPF?
  Notice that I do not change the window height: </p>
  
  <p><a href="https://i.stack.imgur.com/jCgPe.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/jCgPe.png" alt="http://i.stack.imgur.com/jCgPe.png"></a></p>
  
  <p><a href="https://i.stack.imgur.com/Q0V6X.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Q0V6X.png" alt="http://i.stack.imgur.com/Q0V6X.png"></a></p>
  
  <p>How can I disable this "feature" of WPF (or why does it do this?)</p>