title: Scrolling a listbox with page up/down
body: <p>I had an <em>ItemsControl</em>, which you could use page up/down buttons to scroll expectedly. I switched it with a <em>ListBox</em>, to apply (thru triggers) a new DataTemplate when an item is selected. </p>
  
  <p>Everything works fine, until using pageup or pagedown buttons. Instead of scrolling one page, it scrolls till the end or the beginning. </p>
  
  <p>My previous attemps:</p>
  
  <ul>
  <li>Not changing the item height when DataTemplate changes</li>
  <li>Removed IsSelected=True trigger completely</li>
  <li>All SelectionMode values</li>
  </ul>
  
  <p>Do I miss something trivial?</p>