Yeah a similar issue has occurred to me. I'm trying to book AKL to FRA return, but want to go via LHR on NZ2/1 so i can use some RUs. However the Air NZ booking engine only comes up with single stop routes like through Singapore etc and won't let me choose NZ1/2 the whole way. You would think they would want to offer customers the option of maximizing the number of NZ metal flights??? What is up with this???