Qt webengine leaks its WebEngineQuickWidget

#include <QtWidgets/QApplication>
#include <QtWidgets/QWidget>
#include <QtWebEngineWidgets/QWebEngineView>

int main(int argc, char** argv)
{
    QApplication app(argc, argv);

    {
        // tlw: red.
        QWidget tlw;
        tlw.resize(640, 480);
        tlw.setStyleSheet("QWidget { background-color: red; }");

        QWebEngineView webview(&tlw);
        webview.setGeometry(0, 0, 640, 480);
        webview.setUrl(QUrl("chrome://gpu"));

        tlw.show();
        app.exec();

        QWidgetList before = QApplication::allWidgets();
        assert(before.size() == 3); // tlw + QWebEngineView + internal QQuickWidget
    }

    // internal QQuickWidget leaks.
    QWidgetList leaking = QApplication::allWidgets();
    assert(leaking.size() == 0); // actual size() is 1. expect 0.
    return 0;
}