You could argue that there is a "moral hazard" in allowing Infratil to buy back the perpetuals at the discounted price.

Market "convention" is that perpetuals are rarely "perpetual". They are usually redeemed, in full, at some point. Infratil controls this "intervention" - given they are profiting from collapse in bank bill swap rate given to the real market risk price - there is moral hazard in their at market purchases.