[GAMEPLAY] Rammus taunt on Zed didn't taunt him

I was playing a ranked game on SR. As I was ganking mid lane I taunted Zed (The orangish taunt effects went off) but he proceeded to walk towards my mid laner and ult him without any hindrance from my taunt. My mid lane Vik'tor was also shocked by Zed attacking him immediately after getting taunted.

I don't really have many friends to test and try to reproduce this bug. As far as I remember I don't believe it happened again, but I'm not sure how often I taunted Zed later in that game.