Invisible abilities when cast in bushes.

I can understand if it will hide the hit box when I am outside of it. But the fact that the entire ability goes invisible is pretty irritating. I'll explain.

I was playing top lane. The enemy Leona came to gank me. I ran toward the bushes and I see her do her ult animation. I step into the bushes a milisecond after and I just get stunned. Her ability has a delay, this is why it is a problem for me. I was walking in the bushes(I was inside the bushes) and I couldn't see where her ult was coming down.