title: Items added to a Panel are overlapping.
body: <p>When I'm adding items (<code>RadioButtons</code>) to a panel, they are displayed on top of each others :</p>
  
  <pre><code>foreach (var item in items)
  {
     this.ContentPanel.Children.Add(new RadioButton() { Content = ... );
  }
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/8Q89E.png" alt="enter image description here"></p>
  
  <p>Why is that and how can I make them appear on top of each other ?</p>