title: WindowsFormsHost doesn't resize panel
body: <p>Hi I am trying to host a Panel in a WindowsformsHost control as follows:</p>
  
  <pre><code>    &lt;DockPanel LastChildFill="true" Grid.Column="1" Grid.ColumnSpan="2"&gt;
         &lt;WindowsFormsHost Name="FormsHost" Background="Aqua" Height="{Binding ElementName=RootWindow, Path=ActualHeight}" Width="{Binding ElementName=RootWindow, Path=ActualWidth}"&gt;
              &lt;wf:Panel Dock="Fill" x:Name="basePanel" AutoSize="True" /&gt;
          &lt;/WindowsFormsHost&gt;
      &lt;/DockPanel&gt;
  </code></pre>
  
  <p>for some reason the panel doesn't resize when the application does. Has anyone got any ideas?</p>