Good pics there, Jaffa J.
I don't really think that's due to a design fault in the boss. The only way the boss could contribute to that sort of cracking, is if the keyway in the boss is oversize in width, thus allowing/forcing the Woodruff key to tilt in the recess in the crank, and thus overstress the top edge of the recess, when an object strike occurs.
Those corners of the recess are obviously the points where the cracks started, and propagated from.
