This is a Windows specific bug. Attached code snippet can be used to reproduce the problem. The scaling shouldn't effect at all but it is.

QPrinter* printer = new QPrinter();
printer->setOutputFileName("print.pdf");
printer->setOutputFormat(QPrinter::PdfFormat);

QPainter painter(printer);
QPen pen;
pen.setStyle(Qt::DotLine);
pen.setWidth(0);
pen.setBrush(Qt::black);

painter.setPen(pen);
painter.scale(1.95, 1.95);
painter.drawRect(QRect(50, 200, 500, 25));
painter.end();