I see the same thing on my last use, a -1 in the Purchased column on a two sticker flight. Redeemed says -2 and Total says -2 and everything works out right, but that -1 seems like sort of a stray. I just thought it was always there and I'd never noticed it before. No other redemptions this month (lots of AS), the only other line is 4 earned for a 10,000 mile threshold and it doesn't have anything in the Purchased column.