Qt::WA_QuitOnClose has no effect if other windows that don't have the attribute set are present

#include <QWidget>
#include <QApplication>

int main(int argc, char *argv[])
{ 
    QApplication a(argc, argv);
    QWidget w;
    w.setWindowTitle("Close This");
    w.show();
    QWidget w2;
    w2.setAttribute(Qt::WA_QuitOnClose, false);
    w2.setWindowTitle("This should be closed automatically");
    w2.show();

    return a.exec();
}