title: Scrollviewer with stackpanel not working
body: <p>I'm quite new to WPF and I'm sure I'm missing something trivial.
  The scrollviewer does not work when the content of the stackpanel grows. </p>
  
  <pre><code>&lt;ItemsControl&gt;
                  &lt;TextBlock Margin="30,4,0,4" Text="Associated Data: None" Visibility="{Binding SelectedPBL.PBLData.Count, Converter={StaticResource VisibleIfZero}}"/&gt;
                  &lt;ScrollViewer&gt;
                      &lt;StackPanel Margin="30,4,0,4" Orientation="Horizontal" Visibility="{Binding SelectedPBL, Converter={StaticResource CollapsedIfNull}}" ScrollViewer.VerticalScrollBarVisibility="Auto"&gt;
                          &lt;TextBlock FontSize="12" Text="Associated Data:" Visibility="{Binding SelectedPBL.PBLData.Count, Converter={StaticResource CollapsedIfZero}}"/&gt;
                          &lt;ItemsControl FontSize="12" ItemsSource="{Binding SelectedPBL.PBLData}" &gt;
                              &lt;ItemsControl.ItemTemplate&gt;
                                  &lt;DataTemplate&gt;
                                      &lt;WrapPanel Margin="20,0,20,0" Orientation="Horizontal"&gt;
                                          &lt;TextBlock Margin="0,0,10,0" Text="{Binding Path=Key, StringFormat=({0})}"/&gt;
                                          &lt;TextBlock Text="{Binding Path=Value}"/&gt;
                                      &lt;/WrapPanel&gt;
                                  &lt;/DataTemplate&gt;
                              &lt;/ItemsControl.ItemTemplate&gt;
                          &lt;/ItemsControl&gt;
                  &lt;/StackPanel&gt;
                  &lt;/ScrollViewer&gt;
              &lt;/ItemsControl&gt;
  </code></pre>