QWidget::windowState() gets out of sync

#include <QtWidgets>

static QString windowStateString(Qt::WindowStates states)
{
    QStringList str;
    if (states & Qt::WindowMinimized)
        str += "Qt::WindowMinimized";
    if (states & Qt::WindowMaximized)
        str += "Qt::WindowMaximized";
    if (states & Qt::WindowFullScreen)
        str += "Qt::WindowFullScreen";
    if (states & Qt::WindowActive)
        str += "Qt::WindowActive";
    if (states == Qt::WindowNoState)
        str += "Qt::WindowNoState";
    return str.join(",");
}

class Window : public QWidget
{
protected:
    void changeEvent(QEvent *event)
    {
        QWidget::changeEvent(event);
        if (event->type() == QEvent::WindowStateChange)
            setWindowTitle(windowStateString(windowState()));
    }
};

int main(int argc, char* argv[])
{
    QApplication app(argc, argv);
    Window w;
    w.showMaximized();
    return app.exec();
}