setting global style sheet in main.cpp

When trying to set a font size for QWidget globally with a stylesheet in main.cpp on Windows 8 and Windows10 (maybe other versions are affected too, i only had these two for testing) and showing the main window maximized, the window is not set to maximezed, although the window title shows the maximized icon.

As long as no font size for QWidget is set in the stylesheet everything is ok and window is shown maximized

code ex:

int main(int argc, char *argv[]) {
QApplication a(argc, argv);
QString style= "QWidget

";
QApplication a(argc, argv);
a.setStyleSheet(style);
MainWindow w;
w.showMaximized(); // this does not show a maximized window
}

If font size is set as application stylesheet in MainWindow it works as expected