Fails applying a ThemedResource in a custom control.

[mcNets]

I have a custom control derived from a Panel. I want to be able to change the theme between Dark and Light.

I've created a ThemedDictionary and I added it to the App.xaml merged dictionaries.

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:WinUIThemedResource">

	<SolidColorBrush x:Key="BG_Brush_Light" Color="LightGray" />
	<SolidColorBrush x:Key="BG_Brush_Dark" Color="#00243f" />
	<SolidColorBrush x:Key="BG_BorderBrush_Light" Color="Black" />
	<SolidColorBrush x:Key="BG_BorderBrush_Dark" Color="White" />

	<ResourceDictionary.ThemeDictionaries>
		<ResourceDictionary x:Key="Light">
			<StaticResource x:Key="BG_Brush" ResourceKey="BG_Brush_Light" />
			<StaticResource x:Key="BG_BorderBrush" ResourceKey="BG_BorderBrush_Light" />
		</ResourceDictionary>
		<ResourceDictionary x:Key="Dark">
			<StaticResource x:Key="BG_Brush" ResourceKey="BG_Brush_Dark" />
			<StaticResource x:Key="BG_BorderBrush" ResourceKey="BG_BorderBrush_Dark" />
		</ResourceDictionary>
	</ResourceDictionary.ThemeDictionaries>
</ResourceDictionary>

I'm using ActualThemeChanged to set the resources, but it never changes.

public sealed partial class MyPanel : Panel
{
    private Border _border;

    public MyPanel()
    {
        Children.Add(_border);
        ActualThemeChanged += (_,_) => ApplyThemedResources();
        Loaded += (_, _) => ApplyThemedResources();
    }

    private void ApplyThemedResources()
    {
        _border.Background = (Brush)Application.Current.Resources["BG_Brush"];
        _border.BorderBrush = (Brush)Application.Current.Resources["BG_BorderBrush"];
    }

I'm changing the theme using FrameworkElement.RequestedTheme and FrameworkElement.ActualTheme:

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        var elem = MainPanel as FrameworkElement;
        elem.RequestedTheme = elem.ActualTheme == ElementTheme.Dark ? ElementTheme.Light : ElementTheme.Dark;
        SetThemeName();
    }

NOTE: This code works on Uno Platform (Desktop and Wasm)

Am I doing something wrong?

I've added a minimum example to reproduce it.

WinUIThemedResource.zip