title: The Property "inlineXml" can only be set once
body: <p><strong>Multiple LayoutDocument inside LayoutDocumentPane</strong>
  Gives me error - message: "The Property "inlineXml" can only be set once". </p>
  
  <p>Also try using with "LayoutDocumentPaneGroup", gets same error</p>
  
  <pre><code>     &lt;xcad:DockingManager x:Name="DockManager"&gt;
                  &lt;xcad:DockingManager.Theme&gt;
                      &lt;xcad:MetroTheme/&gt;
                  &lt;/xcad:DockingManager.Theme&gt;
  
                  &lt;xcad:LayoutRoot&gt;
                      &lt;xcad:LayoutPanel&gt;
                              &lt;xcad:LayoutDocumentPane&gt;
                              &lt;xcad:LayoutDocument Title="Exp1"&gt;
                                  &lt;TextBox x:Name="TxtInput1"&gt;                                          
                                   &lt;/TextBox&gt;
                              &lt;/xcad:LayoutDocument&gt;
                              &lt;xcad:LayoutDocument Title="Exp2"&gt;
                                  &lt;TextBox x:Name="TxtInput2"&gt;                                          
                                   &lt;/TextBox&gt;
                              &lt;/xcad:LayoutDocument&gt;
                              &lt;/xcad:LayoutDocumentPane&gt;
                        &lt;/xcad:LayoutPanel&gt;
                   &lt;/xcad:LayoutRoot&gt;
              &lt;/xcad:DockingManager&gt;
  </code></pre>
  
  <p>Any idea what am missing?</p>