Alt key modifier behaves erratically when ApplicationWindow menuBar is set

import QtQuick 2.9
import QtQuick.Window 2.2
import QtQuick.Controls 1.3

ApplicationWindow {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    menuBar: MenuBar {
        Menu {
            title: "Edit"
        }
    }

    Rectangle {
        id: content
        anchors.fill: parent;
        focus: true

        onActiveFocusChanged: {
            console.log("activeFocus: " + activeFocus);
        }

        property int keyboardModifiers : 0

        Keys.onPressed: {
            console.log( "pressed key: " + event.key );
            keyboardModifiers = event.modifiers;
        }

        Keys.onReleased : {
            keyboardModifiers = event.modifiers;
        }

        function printModifiers( modifiers ) {
            switch( modifiers ) {
            case Qt.ShiftModifier:
                return "Shift";
            case Qt.ControlModifier:
                return "Control";
            case Qt.AltModifier:
                return "Alt";
            case Qt.MetaModifier:
                return "Meta";
            default:
                return "No modifier";
            }
        }

        Text {
            text: content.printModifiers( content.keyboardModifiers )
            anchors.centerIn: parent
        }
    }
}