It could be because you made the purchase just before they reported the balance. Happend to me with Amazon. took a month and half to get my first payment due one time.
Starting Score: (11/29/10) TU: 598 - EQ: 616
Current Score: TU: 663 (Walmart 12/31/11) - EQ: 654 (MyFICO 12/26/11)
Goal Score: 700
Take the FICO Fitness Challenge