Update
Hi everyone,
Wanted to jump in share the report back on this. Several months ago we adjusted our systems so that it’s no longer possible to book the SYD-MEL local flight through united.com or our primary agent tools, unless it’s accompanied the appropriate United-operated transpacific segment. Unfortunately the OP's booking occurred before that happened. We've been in touch with him since, but if anyone else happens to find themselves in a similar situation, please feel free to PM me and I’d be happy to put you in touch with the right people to handle the reservation.
Aaron Goldberg
Sr. Manager - Customer Experience Planning
United Airlines