QDateTime::offsetFromUtc() is zero when timeSpec() is Qt::TimeZone

#include <QCoreApplication>
#include <QDateTime>
#include <QTimeZone>
#include <QDebug>

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

    // Appropriate timezone
    QTimeZone systemTimeZone("Europe/Moscow");

    // QDateTime object with appropriate timezone
    QDateTime dateTime(QDate(2014, 6, 18), QTime(17, 00), systemTimeZone);

    // Here is the bug:
    qDebug() << dateTime.offsetFromUtc(); // is 0, that's wrong!
    // but
    qDebug() << systemTimeZone.offsetFromUtc(dateTime); // is 14400, that's right

    return a.exec();
}