Ryze Rune Prison adding Luden's Echo Charge when at 100 stacks

I was messing around with the Ryze changes in a custom game when I noticed that using his W when at 100 Luden's Echo stacks used up the stacks and also instantly put the counter back to 20, sometimes even 40. This did not happen on any of his other abilities that I noticed and I assume is not the intended purpose of the ability. After I noticed the possible bug I remade the custom and tried to recreate it, which I was successful in doing.