TabbedMdiHost + MVVM + LayoutSerialization

Hi, I have this docking.
Where I have both the tools and the documents. When I go to deserialize it only restores the tools. If I switch to mdi, the layout is restored correctly.
Why ?

<docking:DockSite x:Name="DockSite"
                              DockPanel.Dock="Top" MdiKind="Tabbed"
                              DocumentItemTemplate="{StaticResource DockingWindowContentDataTemplate}"
                              DocumentItemContainerStyle="{StaticResource DocumentWindowStyle}"
                              ToolItemContainerStyle="{StaticResource ToolWindowStyle}"
                              ToolItemTemplate="{StaticResource DockingWindowContentDataTemplate}"
                              DocumentItemsSource="{Binding Workspace.Documents, UpdateSourceTrigger=PropertyChanged}"
                              ToolItemsSource="{Binding Workspace.Tools, UpdateSourceTrigger=PropertyChanged}">
                <docking:SplitContainer Orientation="Vertical">
                    <docking:Workspace>
                        <docking:TabbedMdiHost  />
                    </docking:Workspace>
                    <docking:ToolWindowContainer />
                </docking:SplitContainer>
            </docking:DockSite>

 if (args.Node != null)
        {
            var serializedToolId = layoutModel.Tools.Keys.FirstOrDefault(s => s == args.Node.SerializationId);

            if (serializedToolId != null)
            {
                var serializedToolType = layoutModel.Tools[serializedToolId];

                Logger.LogInformation(
                    "Restoring layout for {ToolId} - {Type}",
                    serializedToolId,
                    serializedToolType.ToolType
                );

                var stateSource = layoutModel.States.FirstOrDefault(x => x.ToolId == serializedToolId);

                object? state = null;

                if (stateSource != null)
                {
                    state = stateSource.State.FromJson(Type.GetType(stateSource.StateType));
                }

                var (toolViewModel, toolView) = await _workspaceService.BuildTool(
                    Type.GetType(serializedToolType.ToolType),
                    serializedToolId,
                    state
                );


                if (serializedToolType.ToolTypeEnum == ToolTypeEnum.Document)
                {
                    _workspaceService.Add(toolViewModel);

                    //  args.Window = dockSite.ContainerFromDocumentItem(toolViewModel);
                    args.Window = dockSite.ContainerFromDocumentItem(toolViewModel);

                    args.Window.ContainerDockedSize = args.Node.ContainerDockedSize;

                    if (args.Node.StandardMdiBounds != null)
                    {
                        args.Window.StandardMdiBounds = args.Node.StandardMdiBounds.Value;
                    }

                    args.Window.ContainerDockedSize = args.Node.ContainerDockedSize;
                }
                else
                {
                    _workspaceService.Add(toolViewModel);
                    args.Window = dockSite.ContainerFromToolItem(toolViewModel);
                }


                args.Handled = true;
                // await toolViewModel.OnShownAsync();
            }