Maybe there's a pick swap in it.
Actual thoughts on the trade. BP is leading the league in RBI and probably will the whole year hitting cleanup behind Choo and Votto. BJ Upton is Ike Davis bad. Fister seems legit. Marte I like a lot. Probably should get more for BP, but it's not that bad (not really saying it's good either since it's hard to know what Marte will do rest of season).
Still, even discarding position scarcity, BP is awesome. TSS obviously gets the best player here. Keeper 2B would be hard for me to give up.