style animated scroll bars might freeze(stop animating) if we do a heavy paint event

#include <QtWidgets>
#include <QScrollBar>

class TextBrowser : public QTextBrowser
{
public:
    TextBrowser(QWidget *parent = 0) : QTextBrowser(parent)
    {
        for (int i = 0; i < 100; ++i)
            append(QString(100, 'a'));
        findChild<QScrollBar *>()->installEventFilter(this);
    }

    bool eventFilter(QObject *obj, QEvent *event) override
    {
        if (qobject_cast<QScrollBar *>(obj) && event->type() == QEvent::Paint) {
            QThread::currentThread()->msleep(1000);
        }
        return false;
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    TextBrowser tb;
    tb.show();
    return a.exec();
}