Missing top border of a QtGui.QDateEdit when setCalendarPopup(True) on Mac (OS X 10.9)

date_input = QtGui.QDateEdit()
date_input.setDate(QtCore.QDate.currentDate())
date_input.setCalendarPopup(True)
date_input.setDisplayFormat("MM/dd/yyyy")

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QWidget w;
    QHBoxLayout * layout = new QHBoxLayout(&w);
    QDateEdit edit;
    edit.setDate(QDate::currentDate());
    edit.setCalendarPopup(true);
    edit.setDisplayFormat("MM/dd/yyyy");
    layout->addWidget(&edit);
    w.show();
    return a.exec();
}