Unable to remove/disable size grip in all Widgets/Dialogs on Mac

Unable to remove/disable size grip in all Widgets/Dialogs on Mac. Consider the followin simple example:
#include <QtGui>
int main(int argc, char *argv[]){
QApplication app(argc, argv);
QDialog dlg;
dlg.setSizeGripEnabled(false);
dlg.exec();
return 0;
}

The dialog has still the sizegrip enabled.