Qt seems does not recognize timezone with daylight savings offsets such as 
the time zone offset for Sydney is: AEST-10AEDT,M10.1.0,M4.1.0/3.  and Qt does not seems to recognize this one.

On the other hand, standard time zone offsets like Asia/Shanghai CST-8 can be recognized without any issues.

Following code returns empty for qDebug()<<"Qt Timezone Id="<<systemTime.id();

int main(int argc, char *argv[])
{
qputenv("TZ"," AEST-10AEDT,M10.1.0,M4.1.0/3");
QApplication a(argc, argv);
QTimeZone systemTime= QTimeZone::systemTimeZone();
qDebug()<<"System Timezone ID="<<systemTime.systemTimeZoneId();
qDebug()<<"Qt Timezone Id="<<systemTime.id();
return a.exec();
}