Style sheet border-image does not work on QDialog

The code belows demonstrates that the "border-image" property is not affected for the QDialog, opposite to what is said in the documentation: http://doc.trolltech.com/4.4/stylesheet-reference.html#border-image-prop

//-----------------------------------------------
#include <QtGui>

int main( int argc, char * argv[] )
{
QApplication app( argc, argv );
QMainWindow mainWindow;
QWidget * centralWidget = new QWidget;
mainWindow.setCentralWidget( centralWidget );
QVBoxLayout * layout = new QVBoxLayout;
centralWidget->setLayout( layout );

QString style( "border-image: url(image.png) 5; ");
QDialog dialog;
dialog.setStyleSheet( style );
dialog.show();
return app.exec();
}
//-----------------------------------------------