Indonesia more or less has made it unlawful for adults to hold its citizenship while holding citizenship of another country. [Quite a common type of restriction for countries in Asia and Africa that got independence from European colonial powers.]

If you are an adult with both Australian and Indonesian passports and the Indonesian authorities find out that you have passports indicating citizenship of two countries one of which is Indonesian, there may well be problems.

Tickets separated and passports separated/separately used via a third country that doesn't share much if any passenger data (with authorities in the involved other countries) are the way people manage to try to not end up caught. It works often, but not always.