MapQuickItem + MapboxGl ignores item stack ordering

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I've noticed a strange behavior when using MapboxGL plugin with QML maps (Qt 5.15.2, Ubuntu). I slightly modified MinimalMap example in order to reproduce that:

import QtQuick 2.0
import QtQuick.Window 2.14
import QtLocation 5.6
import QtPositioning 5.6

Window {
    width: 512
    height: 512
    visible: true

    Plugin {
        id: mapPlugin
        name: "osm" // "mapboxgl", "esri", "osm", ...
    }

    Map {
        anchors.fill: parent
        plugin: mapPlugin
        center: QtPositioning.coordinate(0, 0)
        zoomLevel: 14

        MapQuickItem {
            coordinate: QtPositioning.coordinate(0, 0)
            opacity: 1

            sourceItem: Rectangle {
                width: 600
                height: width
                color: "blue"
            }
        }

        MapRectangle {
            color: "red"
            topLeft: QtPositioning.coordinate(0, 0)
            bottomRight: topLeft.atDistanceAndAzimuth(1000, 135)
        }
    }
}

Running this code with osm plugin is ok:

But when it comes to MapboxGL stack ordering is ignored:

Stack ordering is only broken when MapQuickItem stacks below MapRectangle. Is it a bug?