QML: strange "Binding loop detected" warning

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

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

    ComboBox {
        id: combobox

        width: 200
        height: 50

        model: 10

        indicator: Rectangle {
            color: "transparent"
            anchors.verticalCenter: parent.verticalCenter
            anchors.right: parent.right
            anchors.rightMargin: 8
            width: 15
            height: 15
            clip: true
            Image {
                x: (combobox.popup.opened ? 10 : 0)
                y: 0
            }
        }

        popup: Popup {
            //id: myPopup // uncomment to fix the warning
            y: 1 - height
            width: combobox.width
            height: 102
            padding: 1

            contentItem: Item {
                ListView {
                    clip: true
                    anchors.fill: parent
                    model: combobox.model
                    currentIndex: combobox.highlightedIndex
                    delegate: combobox.delegate
                }
            }
        }
    }
}