[GAMEPLAY] While doing Solo Rift Herald, the Eye doesn't take extra damage by Shaco.

I was playing AI and tried to solo Rift Herald a couple of times with Shaco's ult (As playing Shaco), and the Herald's eye only takes a large amount of damage on first hit but then its normal amount. To clarify, trigger Herald with box, Herald destroys box and is attacking clone afterwards, Shaco behind Herald and attacking it. Eye opens, First hit does a large amount of damage, then its back to normal, with the eye still open. It does large amount of damage if i am killing Herald with someone else though, another champion. Not sure if its suppose to do that but i am guessing its not...