Gradient in pdf

[lemma]

Good day. Noticed such a thing. If I draw to pdf any shape with a gradient fill, the fill becomes a picture. If a shape to fill a solid color, it will be a vector object.
I understand that to use native gradient, we need to define USE_NATIVE_GRADIENTS, but in qprintengine_pdf_p.h this definition commented.
Why is it done? Native gradient somehow reflects badly on the pdf file? Or maybe someone knows how to put pdf native gradient?

Code example:
@int main(int argc, char *argv[])
{
QApplication a(argc, argv, false);

QPrinter printer;
printer.setColorMode(QPrinter::Color);
QRect rect(printer.width()/3, printer.height()/3,
           printer.width()/3, printer.height()/3);

QList<QBrush> brushs;

QLinearGradient gradient(rect.topLeft(), rect.bottomRight());
gradient.setColorAt(0.0, Qt::white);
gradient.setColorAt(1.0, Qt::green);

brushs.append(QBrush(gradient));
brushs.append(QBrush(Qt::green));

for (int i = 0; i < brushs.count(); ++i)
{
    printer.setOutputFileName(QString("output%1.pdf").arg(i));

    QPainter painter(&printer);
    painter.setBrush(brushs.at(i));
    painter.drawEllipse(rect);
    painter.end();
}

return 0;

}@

P.S. used Qt 4.8.1, 4.8.5, 4.8.6