Originally Posted by
pauldb
CWS's post and cbagent's contribution to the wiki imply that the bookings are never actually merged, so the inbound leg remains ex-HKG. Seemingly there's only a half-avios repricing, not a cash repricing.
It has to be put under the same booking ref for the 2-4-1 to apply across it though.
EDIT: to add, by all means try it, but I would be very surprised if you have two separate one way bookings with separate PNRs with one 2-4-1 applied across both, that would seem to be against the terms of the voucher.