Traget spells and Invulnerability

Not quite sure where to post this.

Something should me made with target spells that go off and the other going invulnerable. EX: Vayne Condems Master Yi, Yi Alpha Strikes, thus dodging Vayne's E. Vayne just lost half her Mana, her E's on Cooldown, and Yi probably killed her.

Couldn't it be taken in count that the -target- spell went off before the invulnerability? Or refund mana for the skill? It was, literally, a waste of mana.

Your taughts?