We arrived at MEL check-in counter 2 hours before our flights. Issued boarding passes in J with the same seat assignments previously booked. Nothing was said to us at that time. Just before boarding, they called 4 people, including us and explained to us there had been a change in the aircraft (with the new business class config) and that we were downgraded. A$350 comp for each of us. This was ticketed using BA award. When we booked the flight 6 months ago, it showed a new 1-2-1 config seat map, later it was changed to 2-2-2 and apparently the actual flight changed back to the new ac. It's frustrating that they played this game on our way over to Sydney and we ended up in the old business seat.