Master Yi Meditation Makes him Invulnerable

So um yeah I don't think this is what is supposed to happen, but I saw this 4 separate times in a game. I'm mid laning as Lux against a Yi when i get him low, he of course meditates. So I throw my ult at him, FULL IN THE FACE, and nothing happens. He loses no health what so ever. Suffers no damage from a Q, E, and R combo. It also wasn't just with me, a Karma empowered Q failed to do any damage.

I know he takes reduced damage during the meditation, but a full Lux ult right in the face should do at least some damage right? The link above shows a gif of the one I was able to get. I forgot Overwolf takes these with every kill, death, or assist.