Button CornerRadius doesn't work in explicit style when implicit style exists

[jsiemens]

Description

Applies to Windows UWP only.

When you have

• an implicit style on a Button
• an explicit style on a Button containing a CornerRadius set to anything

Then, the CornerRadius gets set to a value of 5, ignoring the value that is set in the explicit style.

Steps to Reproduce

Add some code to a page with both an implicit button style (no key), and an explicit button stlye (has a key).

Add a button that references the explicit style.

Sample code:

    <ContentPage.Resources>
        <Style TargetType="Button">
            <!--<Setter Property="CornerRadius" Value="0"></Setter>-->
            <Setter Property="BackgroundColor" Value="Blue"></Setter>
            <Setter Property="TextColor" Value="White"></Setter>
        </Style>
        
        <Style x:Key="ButtonStyle" TargetType="Button">
            <Setter Property="CornerRadius" Value="0"></Setter>
            <Setter Property="BackgroundColor" Value="Blue"></Setter>
            <Setter Property="TextColor" Value="Yellow"></Setter>
        </Style>
    </ContentPage.Resources>
    
    <StackLayout>
        <!-- Place new controls here -->
        <Label Text="Welcome to Xamarin.Forms!" 
           HorizontalOptions="Center" />
        
        <Button Text="Hello World" Style="{StaticResource ButtonStyle}"></Button>
    </StackLayout>

Expected Behavior

The CornerRadius from the button's explicit style is used. In the example above, the CornerRadius should be 0.

Actual Behavior

The CornerRadius from the button's explicit style is not used. In the example above, the CornerRadius is 5.

Basic Information

• Version with issue: 3.4.0.1008975, 3.4.0.1009999, 3.5.0.62956-pre2
• Last known good version: 3.3.0.912540
• IDE: Visual Studio 2018 15.9.4
• Platform Target Frameworks:
  • UWP: 16299
• Nuget Packages: Just Xamarin.Forms

Screenshots

[samhouts]

Issue5046.zip

[Mikescher]

I can reproduce this bug in the current Xamarin.Forms version (4.1.0.555618) for android and iOS (no idea about UWP, I don't have a WindowsPhone).

Someone should probable add the p/Android and p/iOS labels