Suppose there's a printer named "ZEBRA" declared in the control panel, and I try to use it with the following piece of code :

QPrinter printer;
printer.setPrinterName("zebra");
bool bValid = printer.isValid();

QPainter painter;
bool bBegin = painter.begin(&printer);

Because I used lowercase while the printer is declared in uppercase, isValid() will incorrectly return false. Yet, begin() will return true, and printing will work fine (as it should).

I think QPrinter::isValid() should be case insensitive under Windows.