[GAMEPLAY] Cho Gath rupture/ Malphite ultimate interaction

I was playing a game yesterday where i was playing Malphite in the Top lane vs. a Cho Gath. There was a moment in the game where my jungler came to gank for me and Cho Gath retreated into a lane bush. I used my Malphite ultimate to gap close/ CC him and he cast his Rupture and DURING my unstoppable force ultimate i was knocked up by Cho Gath's rupture. I am not 100% sure if this is a bug or not but i was not personally aware of anything that could stop Malphites ultimate after it has been cast.

To reiterate. Cho ran into a lane bush out of vision. I cast Malphite ultimate and half way through my travel time to the lane bush i was knocked up by Cho's rupture.