This is not QF Staff Travel, but the story is similar to what I'm sure most other airline staff experience re discounted staff travel. I was stuck at LAX for 4 days once - mid-Winter and had just been skiing in Canada. So called staff bookings at UA and they listed me and said the flight was wide-open (airline terminology for not booked out). Unfortunately, staff reservations in Chicago didn't realise that the 747-400 aircraft to SYD/MEL were weight limited at that time of the year because of winds, so those empty seats weren't actually useable. Hence the problem at the airport - heaps of airline staff who'd been skiing saying goodbye to a half-empty aircraft night after night. Then we went back to our own (paid for) motels for another day. Re annual leave: I had a great boss at the time who was fine with me being late back to work: just took the extra time as annual leave. But as an airline employee using staff travel you are expected to manage your flights so you're back on time. For crew rostered, it's no excuse.
It did make me think twice: next time I just bought a cheap commercial ticket - the expense of the motels made the ID90 ticket not a good bargain at all. And remember, while QF allow a confirmed trip for annual leave, most tickets are subload aka subject to load aka standby with complex priority and upgrade codes. The CEO is M1F1 per IATA agreements ie. must ride, first class, confirmed on any airline in the world (who belongs to IATA). Crew on duty travel are always M (must ride) as they're usually positioning for duty - they were the codes at my airline but they're pretty standard - a code 'M' for must-ride, 'S' for subject to load (standby), then an upgrade priority into either J or F. S24/J36 was a pretty cough code, but at the end of the day, if there's a spare seat, you'll get it.
The benefit however though was I was in F for the UA trip, the staff reservations people at UA just assumed when they hear 'staff' that they are UA staff where space available F upgrades were the norm. And I also travelled from Jackson Hole to LAX with some UA crew employees who live in that beautiful part of the world and commute to LAX which is their actual base. I thought attempting it as the same day they were rostered to the MEL/SYD flights was a bit risky, but they said they'd rarely had problems, and I'm sure the airport staff 'bump them up' a bit over others knowing they need to work. The UA staff were universally really nice to other airline staff - not so to paying customers sometimes LOL.