Vi's ult is Interruptable?

Noticed whilst playing a game with Vi that Malphite's ult can stop her ult from going off properly.

How to reproduce: >Be Vi. >Ult Malphite. >Whilst channeling have Malphite ult on top of Vi. >Stops Vi channeling her ult.

I wasn't sure if this was intended or not although I assume it's not because the description of Vi's ult reads;

"Target's an enemy champion and chases it down, knocking it up for 1.25 seconds, dealing X (+X) physical damage. While charging, Vi cannot be stopped and will knock aside enemies in the way, dealing 75% damage to them."

Thanks in advance. :)