MSBS Retention Benefit Repayment

I am a serving Defence member under the Military Super Benefit Scheme (MSBS). At 15 years of service members are entitled to a Retention Benefit if the Rank of Sergeant (for enlisted ranks) or Major (or equivalent for Commissioned Officers). The intent is for the member receiving this Retention Benefit to continue a further 5 years of service.
If you choose to terminate service voluntarily or through disciplinary actions, the current policy is that the member is required to repay the pre-taxed amount of the benefit based on a pro rata of service remaining under the Retention Benefit Scheme.
My question is how can a member be forced to repay monies which were taxed and never seen by the member?
Wouldn't these monies be sought by MSBS for reimbursement from the ATO?
Is it possible that the Scheme is double dipping? That is forcing members who decide to terminate service prior to the additional 5 years service under the Retention Benefit to pay back taxes already paid by the member then seeking reimbursment again from the ATO?
If a member seeks to change careers and depart the Defence Force, the reapyment bill can easily be more than what the member received in their bank account. How is this possible, or even legal?
Are there any avenues to deal with this?
Please advise?

Thank you in advance.

Being an ex-military member and having taken this benefit I undertook a lot of research into this particular issue. What you have to understand is that the military along with MSBS wants to make it difficult for the member to reneg on the member taking the benefit so they have put the liability on to the member to pay back the whole amount (pro-rata over time) and then the member to apply to the tax office for reimbursement.    At the time I also spoke to the ATO who said the tax implications were with the individual.    
I am not a lawyer.