With the oneworld Explorer, the "no backtracking" rule has to do with backtracking between continents, not within continents. Thus DFW-LAX-HKG-BKK-HKG-PEK-HKG-LHR-IST-LHR-YVR-DFW is a perfectly legal xONE3 routing. DFW-LAX-SYD-HKG-SYD-SIN-LHR-LAX-DFW is not (also 4 continents, but who's counting?)