As can be viewed on the CASA register of aircraft, some Jetstar A320's are owned by Qantas, some are owned by leasing companies.
My guess is, Jetstar(Qantas) is choosing to end leasing arrangements with some of their A320's and replace them with brand new Jetstar HongKong, Qantas owned, A320's. That's where the 'flexibility' comes into play. It's more then likely not what they wanted to do but it is an easy option for them to take.
Jetstar HongKong(failure), Japan(failure), Vietnam(failure) and Asia's(barely break even) investment in their 40-50 airframes would more then pay for the Qantas airframes that have been deferred/cancelled/retired and not replaced, and more then make up the 1/6th of group revenue that the spin doctors say Jetstar franchises produce.