Malzahar ult gets canceled by zac ult/garen q while not being cced.

I ulted in this scenario garen (or tried to click on him) and i' certainly sure i didn't cancel it myself by doubleclick. I was not in the zac ultimate and Malzahars Passive was still up so i got not cced. 1st Explanation: I hit not garen but zac cause they were close and his ult canceled mine. Problem: Malzahar Ult is a Surpression. i know certain abilitys like malphite ult can't be cancelled and zac is untargetable during his ult. so either i rly hit garen cause he was untargetable and got caneceld randomly (bug). or i hit zac but it did't cancel his ult (bug?). his first cast makes him immune to cc but before (and after that?) he shoulnd't? 2nd Explanation: I hit Garen and either just the moving of People with zac or the animation/use of garen q on one target (not on malz self) canceled it. problem: Lolwiki says nothing that garen is cc imune during his q. and zacs doings had nothing to do with me using malz ult on garen. zac ults enemies away, not allies like a ryzeult, who rly could save allies.

here a slowmoclip again: https://webmshare.com/nZYjN

I think in slowmo you rly see i ulted garen. the cancel of malz ult definetly a bug. even for selfcanceling (my fault/server fault my counting my casst of r doubel?) this happened to fast. like not even 1 s my ult was on.