TemplateBinding to ICommand property not work

Describe the bug TemplateBinding doesn’t work for the ICommand property with Button inside template.

Steps to reproduce the bug

1. Create CustomControl:

class MyControl : Control
{
    public static readonly DependencyProperty MyCommandProperty =
        DependencyProperty.Register("MyCommand", typeof(System.Windows.Input.ICommand), typeof(MyControl), new PropertyMetadata(null));

    public System.Windows.Input.ICommand MyCommand
    {
        get { return (System.Windows.Input.ICommand)GetValue(MyCommandProperty); }
        set { SetValue(MyCommandProperty, value); }
    }
}

1. On root MainWindow:

<StackPanel>
    <StackPanel.Resources>
        <Style TargetType="local:MyControl">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="local:MyControl">
                        <Grid>
                            <Button Command="{TemplateBinding MyCommand}"
                                    Content="RUN"/>
                        </Grid>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </StackPanel.Resources>

    <local:MyControl x:Name="MyControl" />
    <TextBlock x:Name="TextBlock" />
</StackPanel>

1. On code behind MainWindow

public sealed partial class MainWindow : Window
{
    public MainWindow()
    {
        this.InitializeComponent();

        MyControl.MyCommand = new RelayCommand(DO); // Classic RelayCommand
    }

    private void DO(object obj)
    {
        TextBlock.Text = "PRESSED";
    }
}

Expected behavior After clicking on the button, the text must become “PRESSED”. But it’s not. Similar TemplateBindings to other properties work fine.

Workaround Change Command="{TemplateBinding MyCommand}" To Command="{Binding RelativeSource={RelativeSource Mode=TemplatedParent}, Path=MyCommand}"

Version Info

NuGet package version: [Microsoft.ProjectReunion 0.5.0-prerelease] [Microsoft.ProjectReunion.Foundation 0.5.0-prerelease] [Microsoft.ProjectReunion.WinUI 0.5.0-prerelease]

Windows app type:

UWP	Win32
	Yes

Windows 10 version	Saw the problem?
Insider Build (xxxxx)
October 2020 Update (19042)	Yes
May 2020 Update (19041)
November 2019 Update (18363)	Yes
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Xbox
Surface Hub
IoT

[andreaslennartz]

Same issue as in #7003 - still present in 1.2, very annoying bug. Also very surprised to learn that this hasn’t been fixed.

[Soap-141]

Any update on this?