well same thing happened to me, I called and asked for a one way BF upgrade from SJO to HKG (25k miles), they put me on confirmed F for SJO-EWR and the other one showed as waitlisted but no miles were deducted

I already considered the 25k miles MINE and then one day out of the blue (this is still about 6 weeks before the day of the flight) I see a new itinerary in my inbox........I knew it immediately , someone found out or a simple audit told them that there were short of miles somewhere .......and miles were deducted then (it took like a month for them to notice this)

so I would say, do not do a thing, they will find out on their own, remember to let us know what happens though