CX phone reservations are quite good at RTW tickets (better than BA, on par with the AA RTW desk). At least that is the case in the US (just phone the 800 freephone number). Presumably UK reservations are equally trained. Otherwise I've had re-issues done at HKG airport by CX and this takes 10 minutes instead of the hours at some other places, so CX does seem to be better able to handle OWE fares than some other airlines.