Nunu>Yasuo ???

Nunu E can't be spell-shielded. This thread shows up like two times a week since Nunu became meta

That is very much a bug. I just opened a thread to start compiling all of the Yasuo bugs floating around, if you wouldn't mind posting the details it would be appreciated. Nunu's E "Ice Blast" is technically a projectile, and will be spell shielded as well.

List of Abilites blocked by Yasuo: http://leagueoflegends.wikia.com/wiki/Yasuo/Projectiles

Nunu's E (click ability details): http://leagueoflegends.wikia.com/wiki/Nunu#Ice_Blast

Yasuo Bug thread: http://boards.na.leagueoflegends.com/en/c/bug-report/gW3MIuM8-yasuo-bugs

Thank you in advance, and hopefully this clears up/ has cleared up for you considering this is a 4 month old post :)