Popup isn't positioned as expected in certain circumstances

import QtQuick
import QtQuick.Controls.Basic

Window {
    width: 640
    height: 480
    visible: true

    Item {
        id: root
        objectName: "CustomCombobox"
        x: 10
        y: 300
        width: 200
        height: 20

        ComboBox{
            id:control
            anchors.fill: parent
            model: 100

            popup: Popup {
                id: popupList
                x: 0
                y: control.height
                implicitWidth: 200
                implicitHeight: contentItem.implicitHeight
                contentItem: ListView {
                    id:listItems
                    implicitHeight: contentHeight
                    clip: true
                    interactive: true
                    model: control.popup.visible ? control.delegateModel : null
                    currentIndex: control.highlightedIndex
                }
            }
        }
    }
}