QDate.toString() output is not correctly translated under Ubuntu 12.04 (french)

#include <QTranslator>
#include <QApplication>
#include <QLibraryInfo>
#include <QDate>
#include <QLocale>

#include <QDebug>

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

    QTranslator qtTranslator;
    qWarning() << "system locale" << QLocale::system().name() << "app locale" << QLocale().name();
    if (!qtTranslator.load("qt_fr_FR",// + QLocale().name().left(2),
                      QLibraryInfo::location(QLibraryInfo::TranslationsPath)))
        qWarning() << "ERROR";
    qApp->installTranslator(&qtTranslator);
    QLocale::setDefault(QLocale::French);

    QDate dt = QDate::currentDate();
    qWarning() << "DOES NOT WORK: "
               << "dt.toString" << dt.toString(QLocale().dateFormat())
               << "\nDOES NOT WORK: "
               << "locale tostring" << QLocale::system().toString(dt);

    qWarning() << "WORKS FINE"
               << QLocale().toString(dt);

    return a.exec();
}

system locale "fr_FR" app locale "fr_FR" 
DOES NOT WORK:  dt.toString "Thursday, 3 May 2012" 
DOES NOT WORK:  locale tostring "Thursday, 3 May 2012" 
WORKS FINE "jeudi 3 mai 2012" 

system locale "fr_FR" app locale "fr_FR" 
WORKS FINE:  dt.toString "jeudi 3 mai 2012" 
WORKS FINE:  locale tostring "jeudi 03 mai 2012" 
WORKS FINE "jeudi 3 mai 2012"