QML Popup and children are invisible to Spix name/id lookup about spix HOT 1 OPEN

Loader {
    id: popupLoader
    active: false

    Popup {
      id: myPopup

      width: 200
      height: 200

      visible: popupLoader.active
      onClosed: popupLoader.active = false;

      Rectangle {
        id: myRect
        anchors.fill: parent

        color: "red"
      }
    }
}

 setStringProperty("mainWindow/popupLoader", "active", "true");
 wait(1500);
 setStringProperty("mainWindow/myRect", "color", "green");
 wait(1500);
 setStringProperty("mainWindow/popupLoader", "active", "false");