Overridding QMessageBox::paintEvent()

I am creating a custom message box for an application. My object is derived from QMessageBox, but I am overriding the paintEvent() method in order to change its appearance. Curiously, although I do not call the base paintEvent method in my derived method, my custom message box is still being painted with an OK button by default. Here is my code:

class MessageWidget : public QMessageBox
{
    Q_OBJECT

public:

    MessageWidget(QWidget* parent = 0);
    ~MessageWidget();

    void setTitle(const QString& title);
    const QString& title() const;

protected:

    void paintEvent(QPaintEvent* event);
}

MessageWidget::MessageWidget(QWidget* parent) :
    QMessageBox(parent)
{
    setWindowFlags(Qt::FramelessWindowHint);
    setAutoFillBackground(true);
}

void MessageWidget::paintEvent(QPaintEvent* /*event*/)
{
    QPainter painter(this);
    QRect boxRect = rect();

    QPainterPath path;
    path.addRoundedRect(boxRect, 15, 15);
    painter.开发者_运维技巧fillPath(path, palette().window());
    painter.drawPath(path);

    QRect titleRect = boxRect;
    int titleHeight = fontMetrics().height();
    titleRect.moveBottom(titleHeight);

    boxRect.moveTop(titleRect.bottom());
    painter.drawLine(titleRect.bottomLeft(), titleRect.bottomRight());

    painter.drawText(titleRect, Qt::AlignLeft, "Some Text");
}

How is it that other things are being painted when I'm not calling the base paintEvent method?

---

The OK button is not being painted. It's a child QWidget added to the message box. Child widget painting is not controlled in the parent's paintEvent.