Klepto Nasus Bug?

Hi everyone, Mr. Shield Here. As a Nasus main, i've enjoyed using klepto in a lot of different matchups, however, i've noticed it seems to be bugged in the way it procs unless I'm missing something here. Since Kleptomancy makes no mention of an internal cooldown, the obvious conclusion is that it's only "cooldown" is depending on the cooldown of your abilities and your ability to weave autos between each one. I've made a video in practice tool demonstrating how this doesn't seem to be the case as (unless I'm very slow paced in my combos) klepto fails to proc 1-2 times per spell rotation.