Why this code return an invalid date?

QLocale locale("es");
QDate date = locale.toDate("1-Jun-14", "d-MMM-yy");

If debug the locale variable, it is initialized correctly to locale es_ES, but doesn't return the date and date.isValid() returns false.

Please, see http://stackoverflow.com/questions/24091781/qt-qlocale-todate-always-return-invalid-qdate-on-es-locale, where another people tests other locales with the same error.