ManagedSettingsUI ShieldConfiguration.backgroundColor shows square corners in App Switcher

I am seeing a reproducible App Switcher rendering artifact with ManagedSettingsUI shield customization.

When a Screen Time shield is customized with ShieldConfiguration.backgroundColor, the shield appears with an uncropped rectangular background layer in the iOS App Switcher. Square corners become visible around the shield card/background layer.

This disappears when backgroundColor is nil, and reappears as soon as any UIColor is provided. I also observed the same behavior in another Screen Time app that customizes its shield background, so this does not appear to be specific to my app.

Minimal repro:

1. Create an iOS app using FamilyControls, ManagedSettings, and ManagedSettingsUI.

2. Add a ShieldConfigurationDataSource extension.

3. Return a ShieldConfiguration with backgroundColor set to any UIColor.

4. Shield an app and open the shielded app.

5. Open the iOS App Switcher.

Example:

return ShieldConfiguration(

    backgroundBlurStyle: .regular,

    backgroundColor: UIColor(red: 246/255, green: 238/255, blue: 227/255, alpha: 1)

)

Expected:

The shield background should be clipped consistently with the App Switcher card/screen corner mask.

Actual:

The shield background appears as a full rectangular layer in the App Switcher, exposing square corners.

Control tests:

• backgroundColor = nil: no square-corner artifact.

• backgroundColor = UIColor(...): square-corner artifact appears.

• The issue occurs regardless of backgroundBlurStyle, including nil, .regular, and .systemUltraThinMaterialLight.

I filed this through Feedback Assistant as well. Has anyone found a workaround that still allows a custom shield background color?