onTapGesture is working for finger, but not Pencil

Here's a weird one. Do I need to do something different to handle Pencil taps, or is this a bug?

The following code shows a standard `Button`, and a few of custom Views called `SelectButtons`. The `Button` registers a tap with a Pencil or finger, as expected. The `SelectButtons` only work with my finger, on my iPad Pro. The Pencil taps don't register.

struct ContentView: View {
    let nums = [1,2,3]
    @State var selected: Int = 1
    var body: some View {
        VStack {
            Button(action: { print("Test button tapped")}) {
                Text("Test button")
            }
            ForEach(nums, id: \.self) { num in
                HStack {
                    SelectButton(num: num, current: self.$selected)
                    Text("Number \(num)")
                }
            }
        }
    }
}

struct SelectButton: View {
    let num: Int
    @Binding var current: Int
    var isSelected: Bool { current == num }
    var body: some View {
        ZStack {
            Circle().inset(by: 5).stroke()
            Circle().inset(by: 7).fill(isSelected ? Color.blue : Color.clear)
        }.frame(width:40, height:40)
         .onTapGesture {
            print("SelectButton.onTapGesture \(self.num)")
            self.current = self.num
        }
    }
}