I have the same problem, but not with my address.

I used other credit card to make my booking through SPG.com before I got my SPG AMEX. I am pretty sure that I updated my credit card information ever since I got the SPG AMEX.

Recently, I have to pay attention to whether the right CC is used for the reservation, as several of them have been charged to the previous card on file, which means no 2x starpoints for the room charge.