It is never the ticketing airline's problem in the same way that it would not be Flight Centre's problem if it was a booking made with Flight Centre
QF is simply acting as a travel agent
The operating carrier of the affected flight is always the one responsible for handling the issue. Where a schedule change occurs, then the travel agent may need to reissue the ticket and for this they are responsible but it is the operating carrier's responsibility to get passenger to their destination
It is no different in AU than it is in the EU - for EU rules that spell it out have a look at the EU261 regulation