title: Button click event is not fired on first click when place inside popup
body: <p>I have placed a calendar control and a button control inside a popup control.</p>
  
  <p>The problem I am facing:</p>
  
  <ol>
  <li>Popup control is opened by an toggle button click.</li>
  <li>After opening the popup control, I tried to select the date in the calendar on mouse click, now the calendar receives focus.</li>
  <li>Now I'm trying to click the button in the popup, but the button click event fires only on the second click.</li>
  </ol>
  
  <p>The problem is that on the first click the popup receives focus and only on the second click the event triggers.</p>
  
  <p>Code</p>
  
  <pre class="lang-xml prettyprint-override"><code>&lt;Popup
      x:Name="Popup"
      Grid.Row="1"
      AllowsTransparency="True"
      Focusable="True"
      IsOpen="False"
      Placement="Bottom"
      PlacementTarget="{Binding ElementName=Border}"
      StaysOpen="False"&gt;
      &lt;Border&gt;
          &lt;StackPanel&gt;
              &lt;Calendar&gt;&lt;/Calendar&gt;
              &lt;Button Click="Button_Click"&gt;&lt;/Button&gt;
          &lt;/StackPanel&gt;
      &lt;/Border&gt;
  &lt;/Popup&gt;
  </code></pre>