There's more to this . We tracked down the culprit to this 'double' points thing even though a different FF number is given at the return.

BA's system and BA's staff. A friend just flew from London to Toronto on CP. (BA checks-in CP flights). The AA number is printed on the Boarding pass - but 4 days later, the points went to his CP account which he credited his flight over.

I guess the only way to guarantee that the points are posted properly is to : 1) Make two seperate bookings, 2) Scream at the staff.