By my reading of the latest rules:
http://www.oneworld.com/content/libr..._15may2007.pdf
I think you are right and QF may not be right. But in any case, why not fly LAX-MEL x ADL..... and it won't be an issue anyway - since your origin point is SYD.
Others may suggest that you should go through AA to minimise fuel fines.
(PS: don't you hate it in SYD when the sky clears as the weekend is over!)