Mordekaiser Mace of Spades Bug [Gameplay]

Oftentimes, I will notice that when using Mord's Q (Mace of Spades) on a minion, it will not 'echo' to other additional nearby targets, even when such targets are within range. I've noticed this many time in the last week or so, and I've noticed it happening both when the additional targets were close (but not immediately next to) the initial target, as well as when targets were close and immediately next to the initial target. I've noticed this mostly with lane minions. I can't say it's not happening with champions, but I've not noticed it if it is.