Reproducible with the following example. On Windows, this prints "Times" twice, even though there is no such font on the system (only "Times New Roman", which is the font used in the label).

#include <QtGui>

int main(int argc, char **argv)
{
QApplication app(argc, argv);

QFont font("Times");
QFontInfo finfo(font);
qDebug() << finfo.family();

app.setFont(font);

QLabel label(0);
label.setText("Foo");
label.show();

qDebug() << finfo.family();

return app.exec();
}