Cho' goth ult goes on CD without doing damage/getting a stack

Hello,

I have been a Cho' goth main for multiple years and have noticed this issue occur more frequently (occurred twice in a weekend). As an example, I ult minions to get his passive stacks. However, there is about a .25 second period where if I ult the minion, but the minion dies in another manner (tower shot), then my ult will go on CD (the full cd and not the half) and I will not get any stacks. Please fix!