My issue was with my recent DONE3. The ticket was set up with CX Japan. While it was on hold awaiting my new passport arriving (QR wanted all APIS and passport details before they would ticket their flights, so the ticket couldn't go ahead until the passport arrived), the flight number on LAX-IAH changed (AA coded, US operated). The number should have updated when the change was put through. It didn't. So I had to get the flight number sorted out and I wanted to change to the later flight.

When doing changes on oneworld tickets, oneworld says to talk to the carrier of your next flight - regardless of ticketing carrier. So I spoke to AA at JFK.
They said they couldn't do anything, talk to CX.
I contacted CX. They said "we don't operate LAX-IAH. Go talk to AA"
Spoke to AA again at SFO. They said they'd like to make the change, but their systems weren't yet able to change US operated sectors. Talk to US.
When I spoke to US...
They said everything from "not our flight" and "not our ticket" to "can't change award bookings". (I'd like to know how they thought it was a CX issued award booking, when it had a QF FF number)

After being bounced around between CX, AA and US, I finally got the UK CX office to sort it out.