[GAMEPLAY] Mundo's Q heal bug

Mundo's Q should heal half the health it uses if it hits the target and the full amount if it kills the target. Right now when Mundo kills a target with Q it heals only half of the used amount. Doesn't matter what level you are, what level the ability is, or what items you have (although spirit visage of course increases the heal), the bug still appears. It doesn't seem to be based on any runes, I have tried many different combinations and keystones, but since i can't test this without any runes, I can't be 100% sure. Link is a gif that I took from one of my testings. The results were identical in all of them though.