It is "FLAT" it is just verticle instead of horizontal!!
I have learned that it really doesen't matter much unless you have it leanining on a big angle, and also the shorter (5' or less) boards don't warp much if you can keep all the sides exposed to air more or less. Even if you store lumber horizontaly you should put stickers between the layers for air movement.
Rog
PS one of my pet peeves is people who don't understand that "flat" and "level" are NOT the same things.
