Found this which someone might find useful
http://www.ausbt.com.au/fly-jetstar-s-boeing-787-in-business…
The 'loophole' which lets you score business class at economy prices about because Jetstar usually doesn't have business class on its Melbourne-Auckland flights.
As a result, the airline's online booking system has no provision for separating business class seats from economy seats on this route and selling them at a much higher fare.
As far as Jetstar is concerned, when the Boeing 787 flies between Melbourne and Auckland, every seat is an economy seat – even though its Dreamliner has 21 business class seats.
More info in the link about how to pick the best seats
Nice find.