There's been a lot of discussion in regards to when the AF posts to the account etc. Here's my data point.
On my card I put a few small purchases on the card, and the af didn't post on my first billing cycle.
On my wife's card, the first bill closed with no activity on the card, and the af did post to the card.
The only reason I can think of, is that I did change my billing cycle on my card to a later date, but the bill did close on the original date it was set too. I don't know if this is the norm for citi, but that's that.