StackNavigationViewStyle leaves Picker cell gray

I have a master-detail app with a Picker control in the detail for editing a field. After picking the form cell for the picker is gray. This only happens when I use StackNavigationViewStyle: remove that and the cell reverts to normal white.

Is is a bug or my mistake? I am using Xcode 12.1, targeting iOS 14.0, building on macOS 10.15.7.

Here's some sample code.

ContentView is:

Code Block struct ContentView: View {
    @State private var boys = ["Arthur", "Cedric"]
    var body: some View {
        NavigationView {
            List {
                ForEach(boys, id: \.self) { boy in
                    NavigationLink(
                        destination: EditBoyView(boy: boy),
                        label: {
                            Text(boy)
                        })
                }
            }
            .navigationBarTitle("Boys")
        }
        .navigationViewStyle(StackNavigationViewStyle())
    }
}

and the EditBoyView is:

Code Block struct EditBoyView: View {
    public var boy: String
    @State private var name: String = ""
    static var boyNames = ["Arthur", "Bill", "Cedric", "Dean"]
    var body: some View {
        Form {
            Picker("Name", selection: $name) {
                ForEach(Self.boyNames, id: \.self) { choice in
                    Text(choice)
                }
            }
        }
        .navigationBarTitle(boy, displayMode: .inline)
        .onAppear {
            if name == "" { name = boy }
        }
    }
}

If you comment out line 15 of the ContentView then the picker cell is white.