Bug in Gameplay - Thresh Relic Shield Minion Ability Not Working

Issue: The Relic Shield item passive that kills minions under a specific amount of health is not working. It only works and heals the nearby champ if you kill the minion with a what would normally be a last hit. I've tried multiple champions, and have tried thresh multiple times. I have had ample charges, the minions have been below the required, health, and there were nearby champions. I've accounted for all of the variables. Additionaly, it doesn't work on either red or blue side. How to reproduce:

1. Pick Thresh on Blue side.
2. Hit the minion under the specific health level.
3. Make sure you have a charge.
4. Make sure there are nearby champions.