Why is Senna Targetable While Invisible

Melee champs like Garen can walk right up in your E and use their Q or ult on you even though the ability specifically says "Makes you and allies unselectable"....Unless a melee champ walks into the mist then they can see you, doesn't say that anywhere though in the ability description. Also seems kinda dumb to only be effective against ranged champions then. It does add a unique element of surprise in specific situations, but I wish it was a little more versatile.