Not sure if it's a bug or if it's intended... (Yasuo/Mark spell)

I usually play a lot of aram, and so far this week I've been able to play Yasuo 2 times now. In both games (and in games where I wasn't Yasuo myself) I've seen multiple times that the new mark spell is unaffected by Yasuo's wind wall, and has resulted in my death a couple of times where l was at low health. I'm not sure if this was an unintended bug seeing that mark is a summoner spell or if it was an intended game mechanic, but I felt the to bring this up.