Black Cleaver giving two stacks from one auto attack in practice tool

Was testing out black cleaver on kindred. When just equipped with cleaver my autos apply 2 stacks for some reason.

If I wield black cleaver and bloodrazor each auto only applies one stack on one auto

If I wield black cleaver and runaans each auto only applies one stack on one auto

However black cleaver + blade of the ruined king applies 2 stacks on one auto

Black cleaver by itself applies 2 stacks on one auto