Morgana's ult is not disrupted by Ekko's ult

I just wanted to say something cool I found out today. I was playing Morgana mid against Ekko today, and he was going all in on me. I snared, put down my soiled ground, then hit my R, and while it is chaining him, he ults, my roots still WORK as he does his ult (I shield myself while he is transporting) and he is rooted right after he hits his zhonya's, and my ignite with an AA finishes him off. I did not know my ult can still work as he ults. Cool right? :)