Popup does not respect the opacity of its parent item

import QtQuick
import QtQuick.Window
import QtQuick.Controls
import QtQuick.Layouts

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

    Rectangle {
        id: box
        anchors.fill: parent
        visible: true
        color: "#60FFFF00"

        Flow {
            anchors.fill: parent
            Rectangle {
                width: 200
                height: 100
                color: "blue"
                Label {
                    text: "Rectangle outside Popup"
                }
            }
            Item {
                width: 200
                height: 100
                Popup {
                    closePolicy: Popup.NoAutoClose
                    visible: true

                    anchors.centerIn: parent
                    width: parent.width
                    height: parent.height

                    Rectangle {
                        anchors.fill: parent
                        color: "darkgreen"
                        Label {
                            text: "Rectangle within Popup"
                        }
                    }
                }
            }
        }
    }

    SequentialAnimation {
        loops: Animation.Infinite
        running: true
        NumberAnimation {
            target: box
            property: "opacity"
            from: 1.0
            to: 0.0
            duration: 500
        }
        NumberAnimation {
            target: box
            property: "opacity"
            from: 0.0
            to: 1.0
            duration: 500
        }
    }
}