Leak: SwipeDelegate components don't get destroyed, even after the QQmlEngine is destroyed

#ifndef CPPOBJ_H
#define CPPOBJ_H

#include <QObject>
#include <QQmlEngine>
#include <QSet>
#include <QDebug>

class CppObj;
extern QSet<CppObj*> globalObjectRegistry;

class CppObj : public QObject {
    Q_OBJECT
    QML_ELEMENT

public:
    explicit CppObj(QObject *parent = nullptr) : QObject{parent}
    {
        qDebug() << "Constructing" << this;
        globalObjectRegistry << this;
    }

    ~CppObj()
    {
        qDebug() << "Deleting" << this << "with parent" << parent();
        globalObjectRegistry.remove(this);
    }
};

#endif // CPPOBJ_H

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include "cppobj.h"

QSet<CppObj*> globalObjectRegistry;

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    int returnValue;
    {
        QQmlApplicationEngine engine(QUrl("qrc:/main.qml"));
        returnValue = app.exec();
    }
    qDebug("=== QQmlApplicationEngine has been destroyed ===");

    if (globalObjectRegistry.isEmpty())
        qDebug("All CppObjs were deleted at shutdown");
    else
        qDebug() << "These CppObjs were not deleted at shutdown:" << globalObjectRegistry;

    return returnValue;
}

import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.Controls 2.15
import MyCppModule 1.0

Window {
    width: 640
    height: 480
    visible: true

    ListView {
        anchors.fill: parent

        model: ListModel {
            ListElement { name: "Swipe left" }
        }

        delegate: SwipeDelegate {
            id: dg
            width: 640
            Component.onCompleted: console.log(`Created ${dg}`)
            Component.onDestruction: console.log(`Destroying ${dg}`)

            swipe.right: Text {
                id: innerText
                anchors.right: parent.right
                text: "Close the app and check the output"
                Component.onCompleted: console.log(`Created inner ${innerText}`)
                Component.onDestruction: console.log(`Destroying inner ${innerText}`)

                // The QML engine will report that this object gets destroyed, but its C++'s destructor won't get called
                CppObj {
                    id: innerObj
                    Component.onCompleted: console.log(`Created inner ${innerObj}`)
                    Component.onDestruction: console.log(`Destroying inner ${innerObj}`)
                }
            }

            Text {
                id: outerText
                text: name
                Component.onCompleted: console.log(`Created outer ${outerText}`)
                Component.onDestruction: console.log(`Destroying outer ${outerText}`)

                // This object will get destroyed properly
                CppObj {
                    id: outerObj
                    Component.onCompleted: console.log(`Created outer ${outerObj}`)
                    Component.onDestruction: console.log(`Destroying outer ${outerObj}`)
                }
            }
        }
    }
}