WinUI2.7 Rounded corners are removed form the Button when you set the Style to null

[sonnemaf]

Describe the bug

The rounded corners of a Button are removed when a Button has a Style (for example the AccentButtonStyle) and you remove it by setting the Style property to `null'.

Steps to reproduce the bug

Create a new UWP project and add Microsoft.UI.Xaml NuGet package.

Add the following code to the MainPage.xaml

    <StackPanel HorizontalAlignment="Center"
                VerticalAlignment="Center"
                Spacing="12">
        <Button Click="Button1_Click"
                Content="Button 1" />
        <Button x:Name="button2"
                Content="Button 2"
                Style="{StaticResource AccentButtonStyle}" />
    </StackPanel>

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

    private void Button1_Click(object sender, RoutedEventArgs e) {
        button2.Style = null;
    }
}

Run the app and click Button 1

Expected behavior

The Button 2 should have rounded corners

Screenshots

The app starts like this.

If you click Button 1 the rounded corners are removed from Button 2.

NuGet package version

Microsoft.UI.Xaml 2.7.0

Windows app type

• [X] UWP
• [ ] Win32

Device form factor

Desktop

Windows version

No response

Additional context

No response

[StephenLPeters]

Very strange... the button does have the correct "DefaultButtonStyle" from winui2, you can tell from the bottom edge border being a bit darker, but the corner radius value lookup seems to have failed... @MikeHillberg or @jevansaks ring any bells?

[lgBlog]