I'm noticing new stuff on the Barclays card page this evening, including in the FAQ;
For the 10% redemption benefit, what happens if I have more than one AAdvantageŽ Credit Card at Barclaycard or another financial Institution?
The maximum number of miles that can be earned from this benefit is 10,000 miles per AAdvantageŽ account. If you have a credit card account at another financial institution that earns this benefit, your miles will be evenly distributed up to the 10,000 annual maximum.