Edited Issue: AvalonDock 3.3: Serialization of hidden panels does not work [22508]

If I try to serialize the layout with two panels hidden the resulting XML will contain an element like this, which obviously is not valid XML and makes deserialization impossible.

```
<Hidden AutoHideMinWidth="100" AutoHideMinHeight="100" Title="Panel_1" ContentId="Panel_1" CanClose="False" PreviousContainerId="f5ef0b3f-a63b-4c9b-9e09-804485d56c53" PreviousContainerIndex="0" AutoHideMinWidth="100" AutoHideMinHeight="100" Title="Panel_2" ContentId="Panel_2" CanClose="False" PreviousContainerId="f5ef0b3f-a63b-4c9b-9e09-804485d56c53" PreviousContainerIndex="0" />
```

The DockingManager uses bindings to show/hide panels:

```
<xcad:DockingManager Grid.Row="1" x:Name="DockingManager" AnchorablesSource="{Binding Panels}" DocumentsSource="{Binding Documents}" AllowMixedOrientation="True" >
<xcad:DockingManager.LayoutItemContainerStyleSelector>
<avalonTest:LayoutItemStyleSelector>
<avalonTest:LayoutItemStyleSelector.PanelStyle>
<Style TargetType="{x:Type xcad:LayoutItem}">
<Setter Property="ContentId" Value="{Binding Model.DataContext.Text}"/>
<Setter Property="Title" Value="{Binding Model.DataContext.Text}"/>
<Setter Property="Visibility" Value="{Binding Model.DataContext.Visibility, Mode=TwoWay}"/>
</Style>
</avalonTest:LayoutItemStyleSelector.PanelStyle>
<avalonTest:LayoutItemStyleSelector.DocumentStyle>
<Style TargetType="{x:Type xcad:LayoutItem}">
<Setter Property="ContentId" Value="{Binding Model.Text}"/>
<Setter Property="Title" Value="Document"/>
<Setter Property="Visibility" Value="{Binding Model.Visibility}"/>
</Style>
</avalonTest:LayoutItemStyleSelector.DocumentStyle>
</avalonTest:LayoutItemStyleSelector>
</xcad:DockingManager.LayoutItemContainerStyleSelector>
</xcad:DockingManager>
```
Comments: ** Comment from web user: BoucherS **

Hi,
This is already fixed.
The fix will be included in v3.4.