QTimeZone::systemTimeZone return invalid timezone

I tried to run this code

QTimeZone test = QTimeZone::systemTimeZone();
qDebug() << "check timezone valid " << test.isValid();

on my mac, I set timezone by 2 different location
Colombo/Sri Lanka and Indi/India. both of them have timezone +05:30
but the result very strange.
when set Colombo/Sri Lanka return timezone valid
when set Indi/India return timezone invalid.
this issue also happened on computer of my customer. they are in India