CanvasVirtualControl inside Grid will refuse to redraw at a certain position

[fourst4r]

Minimal reproducible: canvasvirtualtest.zip
Video: https://github.com/user-attachments/assets/84db3fdb-cc68-40d3-a464-2a4b675030cd

I could only get this to happen with a CanvasVirtualControl inside a Grid with multiple areas. I'm not sure what triggers it to stop redrawing, but the RegionsInvalidated callback just stops getting fired altogether until you size it back down again.

Xaml:

<?xml version="1.0" encoding="utf-8"?>
<Window
    x:Class="canvasvirtualtest.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:canvasvirtualtest"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:canvas="using:Microsoft.Graphics.Canvas.UI.Xaml"
    mc:Ignorable="d">

    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
        <Button Grid.Column="0">BUDDON!</Button>
        <canvas:CanvasVirtualControl x:Name="cvc" Grid.Column="1" RegionsInvalidated="CanvasVirtualControl_RegionsInvalidated"/>
    </Grid>
</Window>

CS:

using Microsoft.Graphics.Canvas.UI.Xaml;
using Microsoft.UI.Xaml;
using System;
using Windows.UI;

namespace canvasvirtualtest;

public sealed partial class MainWindow : Window
{
    private DispatcherTimer _timer;

    public MainWindow()
    {
        this.InitializeComponent();
        _timer = new DispatcherTimer();
        _timer.Interval = TimeSpan.FromSeconds(0.5);
        _timer.Tick += (_,_) => cvc.Invalidate();
        _timer.Start();
    }

    private void CanvasVirtualControl_RegionsInvalidated(CanvasVirtualControl sender, CanvasRegionsInvalidatedEventArgs args)
    {
        foreach (var region in args.InvalidatedRegions)
        {
            using var ds = sender.CreateDrawingSession(region);
            var color = Color.FromArgb(
                0xff, 
                (byte)Random.Shared.Next(0xff), 
                (byte)Random.Shared.Next(0xff), 
                (byte)Random.Shared.Next(0xff));
            ds.Clear(color);
        }
    }
}