Yasuo W blocks poppy ulti

This is extremly stupid issue. Okay guys, yasuo's W is cool skill, I neither have hatred to yasuo nor I play with him, his skillset is fun and kinda unique , his wall is extremly amazing skill. But.... How can this wall stop poppy ulting? Well this is kinda bullshit. There is no counterplay against it. All you need to do is just waiting he casts his wall so you can use your spells. What if a smart yasuo play who realizes it and use his wall really late or trick you? Tell me if there are some counterplays now.

Plus, The skills which have connection with caster champ like lux's ult, Viktor Q, Velkoz ult etc, can pass through his wall but POPPY ULTI CAN NOT. Is this a bug? If not, can someone explain me how this wall exactly works? thanks.