QIBASE Driver: Timestamps with timezones are not stored as UTC

QDateTime fromTimeStampTz(char *buffer)
{
...
    if (!timeZoneName.isEmpty())
        return QDateTime(d, t, QTimeZone(timeZoneName)); // should convert from UTC here
    else
        return {};
...
}

ISC_TIMESTAMP_TZ toTimeStampTz(const QDateTime &dt)
{
    ...
    // dt is local time, but should be converted to UTC
    ts.utc_timestamp.timestamp_time = midnight.msecsTo(dt.time()) * 10;
    ts.utc_timestamp.timestamp_date = basedate.daysTo(dt.date());
    ts.time_zone = qIanaIdToFbTzIdMap()->value(dt.timeZone().id().simplified(), 0);
    ...
}

    auto db = QSqlDatabase::addDatabase("QIBASE", "test");
    db.setDatabaseName("employee");
    db.setHostName("localhost");
    db.setPort(3050);
    db.setUserName("SYSDBA");
    db.setPassword("masterkey");
    QVERIFY(db.open());
    const auto now = QDateTime::currentDateTime();

    QSqlQuery qry{db};
    QVERIFY2(qry.exec(u"select current_timestamp from rdb$database"_s),
             qPrintable(getErrorMessage(qry.lastError())));
    QVERIFY2(qry.isActive(), qPrintable(getErrorMessage(qry.lastError())));
    QVERIFY2(qry.next(), qPrintable(getErrorMessage(qry.lastError())));
    const auto then = qry.value(0).toDateTime();
    QCOMPARE(now.date(), then.date());
    QCOMPARE(now.offsetFromUtc(), then.offsetFromUtc());
    QCOMPARE(now.isDaylightTime(), then.isDaylightTime());

    // this reveals the bug
    QCOMPARE(now.time().hour(), then.time().hour());

QDateTime fromTimeStampTz(char *buffer)
{
...
    if (!timeZoneName.isEmpty())
    {
        // stored timestamp is in UTC
        const auto utc = QDateTime(d, t, Qt::UTC);
        return utc.toTimeZone(QTimeZone(timeZoneName));
    }
    else
        return {};
...
}

ISC_TIMESTAMP_TZ toTimeStampTz(const QDateTime &dt)
{
    ...
    // convert to UTC before storing
    const auto dtUtc = dt.toUTC(); 
    ISC_TIMESTAMP_TZ ts;
    ts.utc_timestamp.timestamp_time = midnight.msecsTo(dtUtc.time()) * 10;
    ts.utc_timestamp.timestamp_date = basedate.daysTo(dtUtc.date());
    ts.time_zone = qIanaIdToFbTzIdMap()->value(dt.timeZone().id().simplified(), 0);
    ...
}