{GAMEPLAY} Nunu's ult Against Braum Shield

I have just played with Nunu. Braum was the enemy support,Late game,I tried to attack Braum and Varuis,i flashed then ult,Braum jumped on Varuis and used shield,Varuis got away from the ult but braum was still in the range with his shield,When ult finished it didn't do any damage for Braum It just broke his shield.We tried me and Braum to do this again and see,I ulted and he used his shield,Same thing happened,Braum shield just broke and didnt take any damage. I see that this is a bug because if you attack Braum from behind while his shield is active,He will take damage,and Nunu's ult is an area damage ,Witch the enemy take damage from all sides.

Hope you fix this if it were a bug,If it wasn't please tell me. Thanks Ult against Shield