Problem when dealing with 4 bytes encoded UTF-8 character

#include <QDebug>
#include <QByteArray>
#include <QString>

int main()
{
    QByteArray ba1 = "鼷"; // 3 bytes encoded UTF-8 charater
    qDebug() << "1: byte count:" << ba1.size();
    QString str1 = ba1;
    qDebug() << "1: unicode char count:" << str1.size(); // Correct result.

    QByteArray ba2 = "𫚭"; // 4 bytes encoded UTF-8 charater
    qDebug() << "2: byte count:" << ba2.size();
    QString str2 = ba2;
    qDebug() << "2: unicode char count:" << str2.size(); // Wrong result. Should be 1.

    return 0;
}