Where you operating scheduled domestic airservices in Vietnam with seats generally available to the public ?
If so was the aircraft wet leased to a Vietnamese operator.
Are Jetstar Australia wet leasing aircraft from Jetstar Asia ?
(A wet lease is a leasing arrangement whereby one airline (lessor) provides an aircraft, complete crew, maintenance, and insurance (ACMI) to another airline (lessee), which pays by hours operated. The lessee provides fuel, covers airport fees, and any other duties, taxes, etc. The flight uses the flight number of the lessee. A wet lease generally lasts one month to two years; anything less would be considered an ad-hoc charter.)
So doesn't it work both ways?
Not necessarily, just because you can do something in one country doesn't mean you can do it in another.
Eg. You can bring fresh meat, fruit, vegetables into Singapore from Australia. Try bringing a single piece of fruit into Australia from Singapore.