About Black Cleaver - Is it a bug?

Usually I go on Pvp.net to shitpost with very little to contribute. This time I have a genuine report on something:

I was playing Ashe on practice mode and got black cleaver, runaans, and BOTRK. When I attacked a dummy, I noticed that I was able to gain 2 stacks with each AA instead of just 1. I wasn't sure if the other items caused it so I kept removing items until all I had was black cleaver and I was still doing 2 stacks per AA. Has anybody else been seeing the same thing lately?