The official planning utility has loads of bugs, and cannot be trusted.

Try the excellent milage monkey tool instead: http://slfft.allhyper.com/0.95/award.htm

Going from BOM to NRT is no problem, as they are in the same region. Backtracking within the same region is allowed.

HKG-BOM is only regional business class, and the flight currently stops in BKK. There will be direct flights as well in the future though, with better timings.

You could also get more miles by going to asia first, and then australia/new zealand. (i.e. EZE-SCL-GRU-JFK-YVR-MEX-DFW-LAX-HKG-BOM-HKG-NRT-HKG-AKL-SYD-LHR-NBO). But HKG-AKL has no first class.