Zac Leap no knockup

I've noticed the past 2 or 3 times I've used zac's E to leap and I just go a very short distance when I hit a target there isn't any knockup but the cooldown is used. It's possible I cancelled it somehow, but the fact it's happened a few times makes me think differently. To replicate bug, use zac's E but charge it very briefly and only land just in front of where you started, if you hit something or someone, there is no knockup but the cooldown is used.