Warwick/Rageblade

I have noticed when you use ult on someone as Warwick, Rageblade doesn't stack. Instead of getting 3 stacks on Rageblade you get none. This is always the case so i don't know if it is a bug or not. It is kinda expected to get 3 stacks on Rageblade when you hit ult. Bug kinda renders item useless on Warwick, not only that u get no stacks, stacks also go on cd for duration, but it could be nice buy if this wasn't the case .