Ah...I was thinking the riser that broke, but it appears it was the limb.
I agree with Bert. It appears there was just too much pressure at the fade out, which can all be worked out when you tiller.
Like Bert said a more even taper on the riser would help (i.e. on a 16" riser, I would have about 6" of transition, a 4" handle then 6" of transition).
I bet when you first had it on the tiller tree the limbs were not tillered and too much pressure was on the fades when you were pulling it... then boom. When you glue a block to the middle of a board it stiffens that section up but also creates a two natural place for the limbs to want to bend when you pull it back (the fades). So thinner fades and slower tillering will help ensure you alleviate those preasure points. So I would try it again and take your time. The riser and glue up job looks really good though! Good luck!