Sheen bug ( no extra damage added on after proc )

Been messing around with Ezreal a bit and noticed that the extra damage sheen is supposed to give isn't going through. I can attack before using an ability and hit for X amount of damage, use an ability to get sheen proc, then attack after the ability and get the same damage as the attack before sheen proc. This happens with all sheen items as well.

This is a pretty damn big bug and destroys a lot of viability for sheen using characters like Ez. Please fix quickly.