title: wpf scrollviewer mousewheel not working with stackpanel
body: <p>I have a stackpanel wrapped with a scrollviewer. inside the stackpanel I've some grids and inside the grids there're stackpanels again and some tiles control by MahApps Metro.</p>
  
  <p>the scrollviewer is working fine if I drag the scrollbar. but mousewheel not working. may be some control is stealing the mousewheel action but I can't feagure out which one. I've tried to scroll mouse wheel while focusing on the scrollbar. but it's still not working.</p>
  
  <pre><code>&lt;ScrollViewer x:Name="TS" Grid.Row="1" HorizontalAlignment="Stretch" HorizontalScrollBarVisibility="Auto" VerticalScrollBarVisibility="Disabled" CanContentScroll="True" PanningMode="HorizontalOnly" SnapsToDevicePixels="True" Background="Transparent"&gt;
      &lt;StackPanel x:Name="TilesPanel" VerticalAlignment="Top" HorizontalAlignment="Stretch" Orientation="Horizontal"&gt;
          &lt;StackPanel.Resources&gt;
              &lt;Style TargetType="{x:Type Grid}"&gt;
                  &lt;Setter Property="Margin" Value="0,50,0,0"/&gt;
              &lt;/Style&gt;
          &lt;/StackPanel.Resources&gt;
          &lt;Separator Background="{x:Null}" Width="110"&gt;&lt;/Separator&gt;
          &lt;Grid&gt;
              &lt;StackPanel&gt;
                  &lt;StackPanel Orientation="Horizontal"&gt;
                      &lt;StackPanel.Resources&gt;
                          &lt;Style TargetType="{x:Type Grid}"&gt;
                              &lt;Setter Property="Margin" Value="10,0,0,0"/&gt;
                          &lt;/Style&gt;
                      &lt;/StackPanel.Resources&gt;
                      &lt;Grid Height="260"&gt;
                          &lt;StackPanel&gt;
                              &lt;StackPanel.Resources&gt;
                                  &lt;Style TargetType="{x:Type StackPanel}"&gt;
                                      &lt;Setter Property="Margin" Value="0,0,0,10"/&gt;
                                  &lt;/Style&gt;
                              &lt;/StackPanel.Resources&gt;
                          &lt;StackPanel Width="247" Height="119"&gt;
                              &lt;Custom:Tile x:Name="Mail" Margin="0" Width="auto" d:LayoutOverrides="Height"&gt;
                                  &lt;Image Stretch="Fill" Source="Res/AppTiles/Mail.png"/&gt;
                              &lt;/Custom:Tile&gt;
                          &lt;/StackPanel&gt;
  
                          //and it goes on like this//
  
                          &lt;/grid&gt;
                        &lt;/stackpanel&gt;
                  &lt;Separator Background="{x:Null}" Width="50"/&gt;
              &lt;/Grid&gt;
      &lt;/StackPanel&gt;
      &lt;/ScrollViewer&gt;
  </code></pre>
  
  <p>Is the grid that's coming in the way? Or is there any other way to use mousewheel in Horizontal Scrollviewer? I just can't figure out. 
  please help.</p>