This is not new. I learned my lesson with those fickle QF schedulers last year when they changed I think it was 4 flights in a row I'd booked before I got the hint. LOL. My solution: Book a flight they are more unlikely to sub on, like MEL-CNS. I did try asking at the gate to get on the 332 flight on one occasion as it was either just before or just after my ticketed departure (I can't remember which). I was given the "Jetstar Glare" and told to go fish, even when I explained my obviously reasonable and valid reason for wanting to change. Maybe a WP could get away with it, but not a nobody alas

Good luck!