Tiller well as sometimes the BL can be weak in compression.
Jawge
To clarify what this means to you Doc, even thought George is totally right, BL is pretty heavy and is really quite stiff for it's mass. So getting a little bend takes a lot of pressure. But, in spite of it's weight and stiffness, it doesn't seem to return well, if over-compressed. iit is weak in compression elasticity, or just likes to fret instead of merely taking set. If you hinge it much at all during tiller, it'll take a bunch of little compression lines or a few bigger frets right in that area and it's not gonna come back for you.
So, just tiller slowly, and really check and exercise your limbs SLIGHTLY, but often, and don't draw it past finished draw weight during tiller.
Despite that, I LOVE BL and have a very high success rate as far as making finished bows in the draw weight I intended with it, and this in spite of the fact that the available wood around here is usually riddle with borer holes and usually requires a lot of heat and messing around to get it untwisted and uncrooked. Good stuff, one of the better quality American bow woods, if you ask me.