Why do I still see you?

[Pembar]

Hey guys,

I have the following code:

QApplication a(argc, argv);
    Widget w;
    w.setMask(QRegion(0,0,w.width(),w.height()));
    w.show();
    return a.exec();

QApplication a(argc, argv);
    Widget w;
    w.setMask(QRegion(0,0,w.width(),w.height()));
    w.show();
    return a.exec();

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The widget still shows up, without the title bars. I find this strange, can someone explain this to me? Thanks