The issue is that when codeshare flights (AC flight number but TG, SQ, LH, NH or some other metal) are booked they show the AC fare class.

When its mapped to the other airlines fare, it maps to a non-earning or discounted fare class.

The problem is that the other airline's fare class is not ever visible (even in the fare rules) and as such you'll never know until you get to the airport to check into the codeshare flight (and you enquire at the transfer desk or at the gate).

There is a long thread on this issue.

http://www.flyertalk.com/forum/air-c...are-class.html