Update:
So my parents spend an hour on the phone with Aeroplan but got it resolved.
The corrected receipt reads (example) AIF: $35 + GST $5 = total $40
Whereas before it read: US Immigration: $5 + US Customs: $10 + 9/11 charge: $10 = total $40.
So in the end, they were charged the correct amount in taxes, it was just that the original receipt was FUBAR. On par for AC's IT, I guess.