Custom paper size doesn't work with native format PDF output on Mac

#include <QtGui>
#if QT_VERSION >= 0x050000
#include <QtPrintSupport>
#endif
#include <QDebug>

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

    QPrinter p;
    p.setOutputFileName("/tmp/test.pdf");
#if defined(Q_OS_MAC)
    p.setOutputFormat(QPrinter::NativeFormat);
#endif
    p.setPaperSize(QSizeF(5, 5), QPrinter::Inch);
    p.setMargins({0,0,0,0});
    qDebug() << p.printerName() << p.paperSize() << p.paperSize(QPrinter::Inch) << p.paperRect() << p.pageRect();
    QPainter pp(&p);
    pp.drawRect(p.pageRect());

    return 0;//a.exec();
}