I know Qantas has bought some used 747-400 from MH. Possibly they are getting some from BA?? Also, it may be to create extra capacity as Qantas is gradually installing its new Inflight Entertainment product into its 747-400s (about time too!)
Megatop is correct, QF is using one or more BA B744 for the next few months while the Qantas B744 fleet is receiving a new IFE system (economy did not have individual screens until now). When the program is completed, the subject plane is going back to BA, thus, it is not in full Qantas colors. The 5 767-300 aircraft being leased long-term by BA to QF have been repainted in QF colors.