UWP - Multiple InkCanvases stacked with IsHitTestVisible = false still capturing inking

Question

I have two InkCanvases stacked and I'd like to get the top to pass inking to the bottom. I set the top to ishittestvisible=false but it still receives the inking. Then as a test I set both to false and the top still gets inking...what am I missing?

I created a blank project and it exhibits the same problem. Here's the code:

MainPage.xaml

<RelativePanel>
    <StackPanel Name="stackPanelButtons" Orientation="Vertical">
        <Button Name="buttonTop" Content="T" Height="50" Click="buttonTop_Click"/>
        <Button Name="buttonBottom" Content="B" Height="50" Click="buttonBottom_Click"/>
        <Button Name="buttonTopHit" Content="TH" Height="50" Click="buttonTopHit_Click"/>
        <Button Name="buttonBottomHit" Content="BH" Height="50" Click="buttonBottomHit_Click"/>
    </StackPanel>
    <InkCanvas Name="inkCanvasBottom" RelativePanel.RightOf="stackPanelButtons" Width="500" Height="500"/>
    <InkCanvas Name="inkCanvasTop" RelativePanel.RightOf="stackPanelButtons" Width="500" Height="500" Loaded="inkCanvasTop_Loaded"/>
</RelativePanel>

MainPage.cs

public sealed partial class MainPage : Page
{
    public MainPage()
    {
        this.InitializeComponent();
    }

    private void buttonTop_Click(object sender, RoutedEventArgs e)
    {
        if(buttonTop.Content.Equals("T"))
        {
            inkCanvasTop.Visibility = Visibility.Collapsed;
            buttonTop.Content = "t";
        }
        else
        {
            inkCanvasTop.Visibility = Visibility.Visible;
            buttonTop.Content = "T";
        }
    }

    private void buttonBottom_Click(object sender, RoutedEventArgs e)
    {
        if (buttonBottom.Content.Equals("B"))
        {
            inkCanvasBottom.Visibility = Visibility.Collapsed;
            buttonBottom.Content = "b";
        }
        else
        {
            inkCanvasBottom.Visibility = Visibility.Visible;
            buttonBottom.Content = "B";
        }
    }

    private void buttonTopHit_Click(object sender, RoutedEventArgs e)
    {
        if (buttonTopHit.Content.Equals("TH"))
        {
            inkCanvasTop.IsHitTestVisible = false;
            buttonTopHit.Content = "Th";
        }
        else
        {
            inkCanvasTop.IsHitTestVisible = true;
            buttonTopHit.Content = "TH";
        }
    }

    private void buttonBottomHit_Click(object sender, RoutedEventArgs e)
    {
        if (buttonBottomHit.Content.Equals("BH"))
        {
            inkCanvasBottom.IsHitTestVisible = false;
            buttonBottomHit.Content = "Bh";
        }
        else
        {
            inkCanvasBottom.IsHitTestVisible = true;
            buttonBottomHit.Content = "BH";
        }
    }

    private void inkCanvasTop_Loaded(object sender, RoutedEventArgs e)
    {
        addInputs(inkCanvasTop);
        addInputs(inkCanvasBottom);
    }

    private void addInputs(InkCanvas inkCanvas)
    {
        inkCanvas.InkPresenter.InputDeviceTypes = CoreInputDeviceTypes.Pen | CoreInputDeviceTypes.Mouse;
    }
}