Menu in a window with a custom title bar pops up incorrectly positioned

import QtQuick 2.12
import QtQuick.Controls 2.12
import QtQuick.Window 2.12

Window {
    id: root
    visible: true
    width: 640
    height: 480
    flags: Qt.CustomizeWindowHint | Qt.WindowMinMaxButtonsHint

    MouseArea {
        property point previousPosition

        anchors.left: parent.left
        anchors.right: parent.right
        anchors.top: parent.top
        height: 40

        onPressed: previousPosition = Qt.point(mouse.x, mouse.y)
        onPositionChanged: {
            root.setX(root.x + mouse.x - previousPosition.x)
            root.setY(root.y + mouse.y - previousPosition.y)
        }
    }

    Rectangle {
        anchors.centerIn: parent
        width: 200
        height: width
        color: 'red'

        MouseArea {
            anchors.fill: parent
            acceptedButtons: Qt.RightButton
            onClicked: menu.popup()
        }

        Menu {
            id: menu

            MenuItem { text: 'Item 1' }
            MenuItem { text: 'Item 2' }
            MenuItem { text: 'Item 3' }
        }
    }
}