Why doesn't Ash's augment 'Teleport Rush' synergize with the finisher kills in Bladestorm?

Like the title says, I got the augment expecting that as long as I kept up doing Bladestorm attacks and incorporating the teleport ability with it, so that is is doing finisher kills everywhere, that his invisibility would be kept up by it.

Imagine my surprise as I see Ash teleporting across the room, backstabbing enemies left and right, and his invisibility still runs out on me.