IMO the 27th June should have been the cut-off. The Share Registry will only be updated on the T+3 - I know this from missing out on a capital raising with TXN - so technically you don't own the stocks until settlement. What if you can't pay?
However, for Tax purposes it will be the date on the Tax Invoice (BUY / SELL Confirmation) which is the day on which you agreed to buy (or sell). The Tax Invoice also includes a GST component... just incase you are trading through a company and can claim the GST back (on the brokerage - not the parcel cost).