Usually they only report once, like clockwork, on your statement date. Maybe since it was a new account, they reported at the opening, and then again on your regular statement date. They reported twice for us in December, and when I called, they were baffled, and updated AGAIN to show the $0 balance.
Try going onto your online account and see when your statement date is, and see if that was the second time they reported. Discover is great about (normally) reporting only on the statement date, and it's the same date every single month. And if that date doesn't work for you, they will change it, although I think that they go by due date, which is the day before.
So our statement date is on the 18th, due on the following 17th. If we wanted our statement date to be the 2nd, I would ask them to change the due date to the 1st. (Hope that makes sense.

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* Credit is a wonderful servant, but a terrible master. * Who's the boss --you or your credit?
FICO's: EQ 781 - TU 793 - EX 779 (from PSECU) - Done credit hunting; having fun with credit gardening. - EQ 590 on 5/14/2007