2 gates at T4 were converted to be 744 capable a few years ago, and QF started to use these (along with an immigration/customs facility in T4). TBIT was short on gates (still is, actually) and QF disliked using the remote stands by the hangars, deplaning to the tarmac and then bus to the terminal. So move to T4 was highly desirable, also T4 was newly refurbished and QF paid millions to complete the lounge in T4 (hence a joint AC/QP). Great move. But then immigration/customs was consolidated to TBIT (connected by sterile tunnel) and no A380 capable gates possible at T4. Also AA adding more widebodies, competing for the few 744 capable gates. So QF moved back to TBIT as gates there opened up. Great tactics, but split operation is never a good thing (and consider the logistics for QF to be split between 2 terminals).

For completeness, I believe QF107 now departs TBIT (LAX-JFK); a rare domestic flight from the international terminal. QF does have some strange flights.