Nostalrius Begins - Quality wow vanilla realm (1.12)

Using Ferocious Bite while Omen of Clarity is procc'd still consumes energy and in some cases consumes the whole energy bar.

Ferocious bite takes 35? energy and then does extra damage for each energy you have after that. When you FB with OoC up, the FB takes no energy, but uses all energy up as "bonus damage".