Persist the Visual Tree when switching tabs in the WPF TabControl

<Window x:Class="PersistTabDemo.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="clr-namespace:PersistTabDemo.ViewModel"
        xmlns:c="clr-namespace:PersistTabDemo"
        xmlns:b="clr-namespace:PersistTabDemo.Behavior"
        WindowState="Maximized"
        Title="MainWindow">
    
    <Window.Resources>

        <!-- Ref: http://msdn.microsoft.com/en-us/library/ms752032(v=VS.90).aspx -->
        <LinearGradientBrush x:Key="LightBrush" StartPoint="0,0" EndPoint="0,1">
            <GradientBrush.GradientStops>
                <GradientStopCollection>
                    <GradientStop Color="#FFF" Offset="0.0"/>
                    <GradientStop Color="#EEE" Offset="1.0"/>
                </GradientStopCollection>
            </GradientBrush.GradientStops>
        </LinearGradientBrush>

        <SolidColorBrush x:Key="SolidBorderBrush" Color="#888" />
        <SolidColorBrush x:Key="WindowBackgroundBrush" Color="#FFF" />
        <SolidColorBrush x:Key="DisabledBackgroundBrush" Color="#EEE" />
        <SolidColorBrush x:Key="DisabledBorderBrush" Color="#AAA" />
        <SolidColorBrush x:Key="DisabledForegroundBrush" Color="#888" />

        <Style x:Key="PersistTabItemStyle" TargetType="{x:Type TabItem}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type TabItem}">
                        <Grid>
                            <Border 
            Name="Border"
            Margin="0,0,-4,0" 
            Background="{StaticResource LightBrush}"
            BorderBrush="{StaticResource SolidBorderBrush}" 
            BorderThickness="1,1,1,1" 
            CornerRadius="2,12,0,0" >
                                <ContentPresenter x:Name="ContentSite"
              VerticalAlignment="Center"
              HorizontalAlignment="Center"
              Content="{Binding Header}"
              Margin="12,2,12,2"
              RecognizesAccessKey="True"/>
                            </Border>
                        </Grid>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsSelected" Value="True">
                                <Setter Property="Panel.ZIndex" Value="100" />
                                <Setter TargetName="Border" Property="Background" Value="{StaticResource WindowBackgroundBrush}" />
                                <Setter TargetName="Border" Property="BorderThickness" Value="1,1,1,0" />
                            </Trigger>
                            <Trigger Property="IsEnabled" Value="False">
                                <Setter TargetName="Border" Property="Background" Value="{StaticResource DisabledBackgroundBrush}" />
                                <Setter TargetName="Border" Property="BorderBrush" Value="{StaticResource DisabledBorderBrush}" />
                                <Setter Property="Foreground" Value="{StaticResource DisabledForegroundBrush}" />
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>


        <DataTemplate DataType="{x:Type vm:TabPageViewModel}">
            <c:DataGridControl />
        </DataTemplate>
        
        <DataTemplate x:Key="templateForTheHeader" DataType="{x:Type vm:TabPageViewModel}">
            <TextBlock Text="{Binding Header}" />
        </DataTemplate>
        
    </Window.Resources>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="25" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>

        <StackPanel Orientation="Horizontal">

            <TextBlock VerticalAlignment="Center">Selected Page:</TextBlock>
            
            <TextBlock 
                VerticalAlignment="Center"
                Margin="5,0,0,0" 
                DataContext="{Binding Tab2}" 
                FontWeight="Bold" 
                Text="{Binding SelectedPage.Header}" />
            
            <Button 
                Margin="20,0,0,0"
                Content="Add Page"
                Width="80"
                DataContext="{Binding Tab2}"
                Command="{Binding AddPageCommand}" />

            <Button
                Margin="20, 0, 0, 0"
                Content="Remove Page"
                Width="80"
                DataContext="{Binding Tab2}"
                Command="{Binding RemovePageCommand}" />
            
        </StackPanel>
        
        <TabControl 
            Grid.Row="1"
            DataContext="{Binding Tab2}"
            b:PersistTabBehavior.ItemsSource="{Binding Pages}"
            b:PersistTabBehavior.SelectedItem="{Binding SelectedPage}"
            ItemContainerStyle="{StaticResource PersistTabItemStyle}"
            />

        <TabControl 
            Grid.Row="2"
            DataContext="{Binding Tab1}"
            ItemsSource="{Binding Pages}"
            SelectedItem="{Binding SelectedPage}"
            ItemTemplate="{StaticResource templateForTheHeader}"
            />
    </Grid>
</Window>