interesting. i re-read your reply, fone, and then went and looked at the SQ award chart, and there is indeed some fine print that is probably applicable (probably what you were referring to).

"Zonal combination includes certain backtracking routes to which the reference fare will not apply. To confirm the exact mileage required, contact KrisFlyer Membership Services."

so perhaps HKG->SIN->LAX is considered back tracking. however, i stand by my comment about the crappy bait-and-switch being pulled here with what is displayed on the itinerary. i mean, it's fine if there are caveats, but damnit, show it as it is.