Why is Morgana's Black Shield selective?

"Rendering her target immune to all crowd control while the shield holds.

Why does it not block Quinn's blind? Why can Leona still pull herself to you?

Not complaining about Morgana as a whole, I play a lot of her, think she's fantastic obviously Black Shield is one of the more sought after and powerful abilities in the game.

Also - am I the only one who sometimes feel her Q hit box is too big, and sometimes feel as if it's too small?