class QDrawComplexControlBug : public QSlider {
    using QSlider::QSlider;    void paintEvent(QPaintEvent* event) override
    {
        QStylePainter p(this);
        QStyleOptionSlider option;
        initStyleOption(&option);
        option.subControls = QStyle::SC_SliderHandle;
        p.drawComplexControl(QStyle::CC_Slider, option);
    }
};

int main(int argc, char* argv[])
{
    auto app = QApplication(argc, argv);
    app.setStyleSheet("QSlider::handle {border:2px solid; border-radius : 5px; } QSlider::add-page {background: #223377; } QSlider::sub-page {background: #883366; }");    
    auto window = new QMainWindow();
    auto w = new QWidget();
    auto layout = new QVBoxLayout(w);
    w->setLayout(layout);
    auto slider = new QDrawComplexControlBug(Qt::Horizontal, w);
    slider->setRange(0, 100);
    slider->setValue(50);
    layout->addWidget(slider);
    window->setCentralWidget(w);
    window->show();    
    return app.exec();
}