normally the cheapest ex-LHR long haul is booked into I fare, which is non-refundable, non-changable. BA runs promotion sometimes and books one leg (normally return leg) into A fare directly.

In this case (assuming outbound I and inbound A fare), am I able to change the inbound flight? My understanding is that I should be able to change it with a fee because I am actually on A fare (no matter how I get this fare). but in reality, I cannot apparently because this is a free-upgrade "I" fare.

I had a dispute with our travel agent and she insisted this is the fare rule for my ticket. But my ticket clearly shows the inbound is A fare. (btw, A fare can be changed with a fee even it is combined with a non-changeable outbound I fare).

Is the travel agent correct in this case? thanks for your inputs.