improvement CPU usage at QProgressBar call setStyleSheet("") method

If one from parent widget of QProgressBar widget have not empty style sheet property (ex., "QWidget{}") repeating calls setStyleSheet("") method of the QProgressBar widget leads to a gradual increasing of CPU usage until capture one core.
Process Explorer show that main thread of process captures CPU time exactly.

============ Code for reproduction ===========

//-------------------- File main.cpp -----------------------------
#include <QtGui/QApplication>
#include <QWidget>
#include <QProgressBar>

#include "stylesheettimer.h"

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QWidget main;
main.setStyleSheet("QWidget{}");

QProgressBar* pb = new QProgressBar(&main);
main.show();

TStyleSheetTimer ssTimer(*pb); //for repeating calls pb->setSyleSheet

return a.exec();
}

//---------------------- File stylesheettimer.h --------------
#define STYLESHEETTIMER_H

#include <QTimer>
#include <QWidget>

class TStyleSheetTimer : public QTimer
{
Q_OBJECT

public:
TStyleSheetTimer(QWidget& stylewidget)
: QTimer()
, m_stylewidget(stylewidget)

{ connect(this, SIGNAL(timeout()), this, SLOT(onTimer())); start(30); //start timer }

private slots:
void onTimer()

{ m_stylewidget.setStyleSheet(""); }

private:
QWidget& m_stylewidget;
};

#endif // STYLESHEETTIMER_H

============ Code for reproduction finish ===========

Note 1: Passing "main" object (that have non-empty SS) to ssTimer constructor do not lead to increasing of CPU usage.
Note 2: Replacing empty argument value "" by valid CSS string (ex., "QProgressBar{}"

Same effect observed for applying empty CSS string to one from ProgressBar-widget's intermediate parents if the parent have empty style sheet property.
Code below creates few parents and leads to the increasing of CPU usage.

===========
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QWidget main;

QWidget* child = new QWidget(&main);
child->setStyleSheet("QWidget{}");

QWidget* child2 = new QWidget(child);
QProgressBar* pb = new QProgressBar(child2);

main.show();

TStyleSheetTimer ssTimer(*child2);

return a.exec();
}
==============
Note 1: Passing "child" object (that have non-empty SS) to ssTimer constructor do not lead to increasing of CPU usage.