Setting a stylesheet on a QGroupBox causes the focus rect of the title not being painted

#include <QtGui>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QDialog w;

    QLineEdit* le = new QLineEdit("Temp label");
    QGroupBox* groupBox = new QGroupBox("some group box");

    groupBox->setCheckable(true);
    QLabel* labelInGroup = new QLabel("in the group box");
    QVBoxLayout* groupLayout = new QVBoxLayout();
    groupLayout->addWidget(labelInGroup);
    groupBox->setLayout(groupLayout);
    QString style = "QGroupBox {font: normal 13px \"Arial\"; } QGroupBox::title {font: normal 18px \"Arial\"; color: rgb(51,51,51); }";
    groupBox->setStyleSheet(style);
    QVBoxLayout* layout = new QVBoxLayout();
    layout->addWidget(le);
    layout->addWidget(groupBox);
    w.setLayout(layout);
    w.resize(500,500);
    w.show();

    return a.exec();
}