Hi. DockingManager.SaveLayout method don't save layout completely. Here is xaml
<AvalonDock:DockingManager x:Name="dockManager">
<AvalonDock:ResizingPanel>
<AvalonDock:DocumentPane x:Name="documentsPane"
SelectedValue="{Binding CurrentDocument}"
SelectedValuePath="DataContext" />
<AvalonDock:DockablePane>
<AvalonDock:DockableContent x:Name="toolboxContent" Title="Toolbox" IsCloseable="False">
<Default:ToolboxView />
</AvalonDock:DockableContent>
</AvalonDock:DockablePane>
<AvalonDock:DockablePane>
<AvalonDock:DockableContent x:Name="outlineContent" Title="Outline" IsCloseable="False">
<Outline:Outline Root="{Binding CurrentDocument.OutlineRoot}"/>
</AvalonDock:DockableContent>
</AvalonDock:DockablePane>
<AvalonDock:DockablePane>
<AvalonDock:DockableContent x:Name="errorsTabContent" Title="Errors">
<Default:ErrorListView ItemsSource="{Binding CurrentDocument.XamlErrorService.Errors}"/>
</AvalonDock:DockableContent>
</AvalonDock:DockablePane>
<AvalonDock:DockablePane>
<AvalonDock:DockableContent x:Name="propertyGridContent" Title="Properties" IsCloseable="False">
<sd:PropertyGridView x:Name="uxPropertyGridView"
SelectedItems="{Binding DataContext.CurrentDocument.SelectionService.SelectedItems, ElementName=root, FallbackValue={x:Null}}"/>
</AvalonDock:DockableContent>
</AvalonDock:DockablePane>
<AvalonDock:DockablePane>
<AvalonDock:DockableContent x:Name="thumbnailTabContent" Title="Thumbnail">
<sd:ThumbnailView x:Name="uxThumbnailView" DesignSurface="{Binding DataContext.CurrentDocument.DesignSurface, ElementName=root, FallbackValue={x:Null}}" />
</AvalonDock:DockableContent>
</AvalonDock:DockablePane>
</AvalonDock:ResizingPanel>
</AvalonDock:DockingManager>
After saving it drops documents pane.