title: Keyboard Focus is not working in textbox added inside the popup
body: <p>When we select any of the TreeNode in WindowsFormHost and then try to type text in textbox shown in popup does not allow to add text since the focus is not lost from the TreeNode. Can i get suggestion on this ?</p>
  
  <p>Code Snippet : </p>
  
  <pre><code>&lt;Window x:Class="WpfApplication2.MainWindow"
          xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:wind="clr-namespace:System.Windows.Forms;assembly=System.Windows.Forms"
          Title="MainWindow" Height="350" Width="525"&gt;
      &lt;Grid&gt;
          &lt;Popup Width="250" Height="300" StaysOpen="True" IsOpen="True"&gt;
              &lt;TextBox Width="100" Height="100"/&gt;
          &lt;/Popup&gt;
          &lt;WindowsFormsHost Width="200"&gt;
              &lt;wind:TreeView&gt;
                  &lt;wind:TreeView.Nodes&gt;
                      &lt;wind:TreeNode Text="Node 1"/&gt;
                      &lt;wind:TreeNode Text="Node 2"/&gt;
                      &lt;wind:TreeNode Text="Node 3"/&gt;
                      &lt;wind:TreeNode Text="Node 4"/&gt;
                  &lt;/wind:TreeView.Nodes&gt;
              &lt;/wind:TreeView&gt;
          &lt;/WindowsFormsHost&gt;
      &lt;/Grid&gt;
  &lt;/Window&gt;
  </code></pre>
  
  <p>Sample Link :  </p>
  
  <p><a href="http://www.syncfusion.com/downloads/Support/DirectTrac/85553/WpfApplication21123581705.zip" rel="nofollow">http://www.syncfusion.com/downloads/Support/DirectTrac/85553/WpfApplication21123581705.zip</a></p>