[Gameplay] Sion soul furnace not registering large monsters

So this is the 2nd time I've encountered this. It's inconsistant, and I can't recreate it deliberately.

Soul furnace was taken at level 1. Even if all creep takes were small creeps, soul furnace bonus HP should be 148, Definitely large creeps taken, and no HP change was seen on taking the large monsters either, so not just a bug with the visual counter.

Steps to recreate: Have a Sion

Potential cause highlighted below, quoted here for convenience:

{quoted}

Hello! I believe I found the cause of this bug. If you level up your W for the first time, in your passive form "Glory of Death", you will be unable to to receive the bonus health upon large minions and large monsters!

To prevent this bug, please avoid leveling up your Soul Furnace (W) ability while in your passive form, "Glory of Death"! ^.^