First of all, this poison has no visual effect at all... basically you get rooted in place with no feedback, unless you run some sort of buff tracker, it gives the impression the game is bugged and doesn't let you move.
Second problem, it also immobilizes you while in mist form, while the skill tooltip clearly states:
"Entering this form removes and grants immunity to all disabling and immobilization effects, but you cannot be healed and your Magicka Recovery is disabled."
Can provide clear video footage if required, but I'm sure Q&A can easily reproduce this.