Just tested it at Gate 37, International Terminal at YSSY. Didn't get a choice to select operators, it just gave me Qantas.
I tried it now, and I got JST, Dnata and Qantas, which is exactly what I expected to get, because JST and Dnata both have full 4 letters matching in the GSX vehicles set, and Qantas is also is assigned to that parking.
And, from what I know, there are no specific "Qantas" gates at Sydney's International Terminal so it Qantas shouldn't have had more probability than others.
The AFCAD as made by Flytampa DOES have a QFA code at Gate 37 so yes, it's correct that Qantas would get a better score, but it's nevertheless displayed as a choice together with JST and Dnata.
Are you sure you are using the latest GSX ? to be absolutely sure you have the latest GSX and the latest vehicles too, download and install in this order:
1) The latest GSX full installer
2) The GSX vehicles update N.5
3) The Couatl 3 Public Beta