Why doesn't Rek'sai go under barrier skills when creating a tunnel

Ok, so I noticed this when I fought enemy champs like and thought about his barrier stun, and thought to tunnel under it to avoid the stun (since, you know, logic tells me since you can tunnel under terrain, then you can tunnel under barriers too), but, somehow, I was stunned and faced veigar's 1-2-3 combo. I tried this again with and his barrier slow. Again, I was affected by the slow. Yet, I could easily get inside and his ultimate. Have not tried yet if I can go underneath and her wall of ice. Wondering if they should add avoiding all skills that give effects when passed through as he creates tunnels or not?