I was doing a relative a favour. They had a complex itinerary, Aussie TA booked, but ticketed via Qantas. Everything I tried to do via my own BAEC log in came back in Aussie dollars. The flight she was going on next was a BA flight.
I understand the link back to Aussie dollars, but BA IT knew it was me doing stuff, from a UK base. Not a problem, and we found a reasonable solution.
Maybe it was the TA booking aspect that locked the currency.