Broken window state after closing a top-level widget

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);

	QMainWindow w;
	w.setWindowTitle("Main Window");

	// setup a top-level widget
	QWidget topLevelWidget;
	{
		QVBoxLayout *const topLevelWidgetLayout = new QVBoxLayout(&topLevelWidget);
		QLabel *const testLabel = new QLabel(&topLevelWidget);

		testLabel->setText("Is this text visible?");
		testLabel->setStyleSheet("background-color: #00FFFF;");
		testLabel->setMinimumSize(200, 200);

		topLevelWidget.setLayout(topLevelWidgetLayout);
		topLevelWidgetLayout->addWidget(testLabel);
	}

	// setup button that shows the top level window
	QPushButton *const openCustomWidgetButton = new QPushButton;
	{
		openCustomWidgetButton->setText("Open Second Window");
		QObject::connect(openCustomWidgetButton, &QPushButton::clicked, [&topLevelWidget]()
		{
			if (topLevelWidget.isVisible())
				return;

			qDebug() << "showing top-level widget";

			topLevelWidget.showNormal();
			topLevelWidget.activateWindow();
			topLevelWidget.raise();
		});
	}

	w.setCentralWidget(openCustomWidgetButton);
	w.show();

	return a.exec();
}