Fixing Blend problem

 From:  Frenchy Pilou (PILOU)
6063.4 
I have trimed a sphere for test the Blend Function
But even result visually seems very good, I am not sure that is 100 % safe ?
I ask the question! Does this a real sphere ? Seems yes but want to be sure! :)

EDITED: 26 Jul 2013 by PILOU