quadrafire,
I have not played too much with the arrow spine and arrows on that bow. It could be the arrow material (carbon). I don't really know for sure. In fact I might go try to shoot some port orford cedar through it at short range next time. I believe wood recovers faster than carbon and I have been shooting exclusively carbon out of that bow.
All of my bows with the exception of one are in the 55-60lb draw range. Now only one of those require differently spined shafts. That's the 67-70lb longbow.