title: Scrolling on ListBox in Popup
body: <p>I have that layout:</p>
  
  <pre><code>&lt;Popup&gt;
      &lt;Border&gt;
          &lt;ScrollViewer&gt;
              &lt;Grid&gt;
                  &lt;TextBlock/&gt;
                  &lt;ListBox/&gt;
                  &lt;TextBlock/&gt;
                  &lt;ListBox/&gt;
              &lt;/Grid&gt;
          &lt;/ScrollViewer&gt;
      &lt;/Border&gt;
  &lt;/Popup&gt;
  </code></pre>
  
  <p>The problem I have is that I can scroll when cursor is above TextBlock and background of border, but I can not when it is above ListBox items.
  ListBox display all items without scroll bar.
  I want that whole ListBox behave as one control.</p>
  
  <p>Why scrolling don't work only above ListBoxes?</p>