QGraphicsView scale bug (sub-widget isn't repaint ?)

Question

Hi,I'm on ubuntu lucid with qt4

QGraphicsView seems don't like scaling + scrolling ,white lines appears when scrolling ,see by yourself:

#include <QApplication>
#include <QtGui>

int main (int argc, char *argv[])
{
    QApplication app(argc, argv);
    QLabel* lab = new QLabel;
    QPixmap img(300,300);
    img.fill(Qt::red);
    lab->setPixmap(img);
    QGraphicsView* viewer = new QGraphicsView(new QGraphicsScene);
    viewer->scene()->addWidget(lab);
    viewer->scale(10,10);
    viewer->show();
    return app.exec();
}

It don't appear with QGlWidget as viewport

EDIT : NOT reproduced on windows 7