I cannot recreate this. I used Sargnhavian Centaur, Centaur Commander, Centaur Archer, Centaur Interceptor, Centaur Savage and Centaur Regulator and they were all receiving +1 DEF from Bliss for each auto she made.
I just tried again. Not sure what I am doing that your not. I used 4 different centaurs (including bliss). I attack with her and the animation and sound go off fine but I only see my centaur commander getting the buff. It's the only one that gets the animation recieving the buff as well. I have double checked other units stats before hand to make sure. They do not get the animation of the buff and their stats stay the same.