Baseline alignment offset when text has fallback fonts

import QtQuick
import QtQuick.Window

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

    Rectangle {
        id: alignItem
        x: 50
        y: 100
        width: 400
        height: 1
        color: "blue"
    }

    Text {
        id: textItem
        textFormat: Text.RichText
        font.family: "Arial Unicode MS"
        font.pixelSize: 50

        text: "a&#29340;&#2339;<span style=\"font-size: 25px\">a&#29340;&#2339;</span><span style=\"font-size: 10px\">a&#29340;&#2339;</span>"

        anchors.baseline: alignItem.top
        anchors.left: alignItem.left
    }
}