Pdf print engine draws an excessive border for objects in images with transparent background

#include <QtGui>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QPixmap pixmap(200, 100);
    pixmap.fill(Qt::transparent);
    QPainter pixPainter(&pixmap);
    QPen pen(Qt::yellow);
    pen.setWidth(5);
    pixPainter.setPen(pen);
    pixPainter.drawLine(10, 10, 100, 10);
    pixmap.save("pixmap.png");

    QPrinter printer;
    printer.setOutputFileName("output.pdf");
    QPainter painter(&printer);
    painter.drawPixmap(pixmap.rect(), pixmap);
    painter.end();

    return 0;
}