I've noticed the exact same thing just this Dec, more than once. I'd buy/pay for an item on, say, 1 Dec. Seller marks as posted on 7th (bit slack but hey we're all busy this time of year) and suddenly payment date changes to 6 Dec instead of 1 Dec. It's as if the system is changing the payment date to the posted date, and losing a day using US time.
I know it's not the sller doing any manipulating, it's gotta be a system thing. I don't think it matters though? I can't think of any way I could get screwed by this happening (maybe I'm not thinking hard enough).
