Clicking Mac title bar doesn't close popup with no parent

#include <QApplication>

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

    QWidget window;
    window.show();

    QWidget popup(NULL, Qt::Popup);
    popup.setFixedSize(100,100);
    popup.show();

    return a.exec();
}

#include <QApplication>

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

    QWidget window;
    window.show();

    QWidget popup(&window, Qt::Popup);
    popup.setFixedSize(100,100);
    popup.show();

    return a.exec();
}