Relic Shield and Kalista

I have run into the problem of not being able to execute low health minions with the Relic shield if there is a Kalista spear sticking out of them. I just got out of a game where I was Leona with a relic shield. I had full stacks on available on my relic shield, both on the icon and 2 orbs around the champion on the screen. However when I went to execute a minion, I would not lose a stack and neither myself or Kalista received the gold for the minion. I did get the 1 gold from an ally killing a minion when I was near. We tried executing minions with no Kalista spears and found that it worked like it was supposed to. The adc and I were in a skype call so we did have communication on which minion I was going to execute. Is anyone else having this problem?