I've had Japan -> Cairns -> Sydney before, and never had issues with duty free alcohol in cabin (I assume that's what is meant here?).
My understanding is, once you get off at Cairns and go through immigration, that's it, you are no longer an international passenger.
Is this not the case nowdays or has something changed? Very relevant for me right now.
Why would security of all things take away alcohol? There are no limits on alcohol carrying on domestic flights. I remember they once wanted me to open up my backpack with alcohol, because I had the samurai whisky and it looks super like a weapon, but then when they saw it, they just laughed, complimented the whisky and let me through.