Assigning to array elements of QQmlListProperty in QML has no effect

BirthdayParty {
    host: Person {
        name: "Bob Jones"
        shoeSize: 12
    }

    guests: [
        Person { name: "Cam Stevens" },
        Person { name: "Janet White" },
        Person { name: "Mahmoud Abdullah" }
    ]

    property var leo: Person { name: "Leo Hodges" }
    property var jack: Person { name: "Jack Smith" }
    property var anne: Person { name: "Anne Brown" }

    Component.onCompleted: {
        guests[0] = leo;
        guests[1] = jack;
        guests[2] = anne;
    }
}