Well, you dont actually 'make me sick'.... but you have to expect airlines to try different tactics to see how people deal with unexpected situations, after all.... thats what we are employed for as cabin crew.
If you cant adjust your approach in an interview when you come across an unexpected change, how are you going to cope in an aircraft when something unexpected happens?
That's probably the way they approach it.... why do you think QF changes their interview process and interview questions every time they hold interviews? If you knew exactly what they were going to do, you'd have an unfair advantage.... you have to learn to think quickly if you want the job !
And, no it's not illegal to change the way you interview.... an employer has the right to interview any way they wish, as long as they dont break E.E.O law, O.H.&S law, and common law.