The total value at the end is correct.
I think that becasue the gift voucher is subject to 0% vat, then the pre vat price is obviously still £65.
Then in the saving, it says a saving of £54.17 before vat. I think this is because it is calculating the hole basket with vat at 20%, therefore a saving of £65 with VAT at 20%.
eg for macbook pro.
£716.00 (ex Vat) 859.20(inc Vat)
£65.00 (ex vat) £65.00 (inc vat)
Basket Subtotal£781.00.
Free Delivery£0.00.
Savings (ex. VAT)-£54.17.
VAT £132.37.
Order Total£859.20.
Total savings (excl. VAT)£54.17
So the order total is correct.
They way to think of it is that you are paying full price for the card, but getting £65 including vat off the Mac. Which saves apple £54.17 but also means £10 ish is saved on their vat bill to the goverment.