Zed shuriken bug?!?

I was playing mid against a champion named zed, but his most powerful ability almost always killed me. it was his shuriken, and it was completely invisible. there was no way for me to see it, and therefore, no way to tell that he was even casting it. it ruined a completely good game, and made defending mid impossible. I believe this may be a bug, as i afterwards watched the ability tutorial of zed's shuriken, and saw red lines to prove that it can be seen.