Unable to LoadFromFile when DockSite is contained within a UserControl

I have an MDI application that successfully saves and loads the docksite state for the main window, however; I have an embedded docksite within a usercontrol.  I subsrcibe to the IsOpen view model property which is triggered when document that contains the embedded docksite is closed via the document close button.  I am able to save the embedded docksite and verify the values are updated.  My view model sets the SerializationId to the name of the class.  When I load the saved state, the state is ignored and no exception if fired.

    <Grid>
        <docking:DockSite 
            x:Name="dockSite"            
            Margin="0"
            Padding="0"
            ToolWindowsHaveTabImages="True"
            ToolItemContainerStyle="{StaticResource ToolWindowStyle}"
			ToolItemTemplateSelector="{StaticResource ToolItemTemplateSelector}"
			ToolItemsSource="{Binding ToolViewModels}"
            >
            <docking:SplitContainer Orientation="Vertical">
                <docking:Workspace>
                    <DataGrid>
                    </DataGrid>
                </docking:Workspace>
            </docking:SplitContainer>
        </docking:DockSite>
    </Grid>

       public MyView()
        {
            InitializeComponent();
            LoadDockState();
        }

        private void UserControl_Loaded(object sender, RoutedEventArgs e)
        {           
            VM.PropertyChanged += VM_PropertyChanged;
        }

        private void VM_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
        {
            try
            {
                if (e.PropertyName == nameof(DocumentItemViewModel.IsOpen))
                {
                    if (!VM.IsOpen)
                    {
                        SaveDockState();
                    }
                }
            }
            catch (Exception)
            {

            }
        }

        private static string DockFilePath
        {
            get
            {
                return string.Format(@"{0}\{1}", MyPath.UserApplicationDataPath, DOCK_FILENAME);
            }
        }

        private void LoadDockState()
        {
            try
            {
                if (File.Exists(DockFilePath))
                {
                    new DockSiteLayoutSerializer().LoadFromFile(DockFilePath, dockSite);
                }
                else
                {
                    string layout = Properties.Resources.ViewDockManager;
                    new DockSiteLayoutSerializer().LoadFromString(layout, dockSite);
                }
            }
            catch (Exception ex)
            {
                Commands.DisplayException.Execute(ex);
            }
        }

        private void SaveDockState()
        {
            new DockSiteLayoutSerializer().SaveToFile(DockFilePath, dockSite);
        }