If QPrinter::setPrinterName() is called after orientation has been set, the orientation is initialized to default on Windows. On Linux the set orientation will be kept even after setting the printer name.

The following code can be used to reproduce the issue:

QPrinter pr;
pr.setPageSize(QPrinter::A4);
pr.setOrientation(QPrinter::Landscape);
pr.setPrinterName(pn); // name of the used printer
qDebug() <<  pr.orientation();