If you use smart cast, and then you go into options and you turn on range indication, so that if you're on a champ like Diana, you can see your skill shot's range, your self casts don't go off.

Load into a match with Lulu (this is a good example of a self casting champ), Make sure you turn on smartcast, your range indication, and you have your keybindings set up for self casting spells.

Attempt to self cast your spells, like Whimsy. Instead of instantly casting the target spell onto yourself, it brings up a range indicator, and then you have to click on yourself to get the spell to go off, which completely negates the point of having self casting key bindings set up to begin with.

I have seen this aswell