Seeker's Armguard glitch

I've found this item to have some serious glitches for a year atleast and still hasn't been fixed nor have I seen anyone post about it so I', addressing it now. So killing a unit grants a stack right? But for some reason I would clear a whole wave of minions and only gain like 1 stack and sometimes just killing one minion grants me a stack, so I'm not sure how that exactly works. Another thing would be undoing it, Just yesterday I had 5/15 stacks on and upgraded it to but then I clicked undo button and got back and it was back to 0/15 stacks? Why idk, glitch? Idk try this item out and if you guys can tell me if you're facing the same problem or not? Thanks