QQuickWidget doesn't properly hide() and show()

#include <QQuickWidget>
#include <QtWidgets>

class HideShow : public QObject {
    Q_OBJECT
public:

    QWidget *subject;
    HideShow(QWidget *subject, int interval) : QObject(subject), subject(subject)
    {
        startTimer(interval);
    }

    void timerEvent(QTimerEvent *)
    {
        if (subject->isVisible()) {
            qDebug() << "hide" << subject->width() << subject->height();
            subject->hide();
        } else {
            qDebug() << "show" << subject->width() << subject->height();
            subject->show();
        }
    }
};

int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    QMainWindow *toplevel = new QMainWindow;

    QUrl source("qrc:quickwidget/rotatingsquare.qml");
    QQuickWidget *w = new QQuickWidget;
    w->resize(300,300);
    w->setResizeMode(QQuickWidget::SizeRootObjectToView);
    w->setSource(source);

    new HideShow(w, 3000);
    toplevel->setCentralWidget(w);
    toplevel->show();
    return app.exec();
}

#include "main.moc"