[GAMEPLAY] Hecarim's E doesn't knock Kalista back during her passive

I was playing Hecarim against a Kalista, and I noticed that when she was moving with her passive, it makes her seemingly invulnerable to Hecarim's e knockback. Hecarim instead just passes through her, dealing damage but without the knockback effect and actually putting him further away from Kalista. To reproduce it, I think the best way is to just let Kalista autoattack and move backwards, as Hecarim's E is activated, then see if Hecarim knocks her back. It occurred twice in the game that I was in, however it did knock her back when she was stationary, say from a stun. It was just during her passive - I don't think this is intended.