macOS: Transparent windows leave permanent outline of initial contents

import QtQuick 2.15
import QtQuick.Window 2.15

Window {
    width: 300
    height: 300
    visible: true
    color: "transparent"
    flags: Qt.FramelessWindowHint
           // | Qt.NoDropShadowWindowHint // WORKAROUND

    Rectangle {
        id: rectangle
        width: 100
        height: 100
        color: "green"

        NumberAnimation on x { to: 200; duration: 2000 }
        NumberAnimation on y { to: 200; duration: 2000 }
    }
}