Passive health stacking on Sion W doesnt stack right!

Hey guys, I have been playing Sion Jungle alot and I've come across some inconsistencies. Either the tooltip isn't showing the health gained from killing minions/monsters/champions properly or even more severly it may not be stacking right. When I jungle sometimes health doesnt stack after killing a monster. Furthermore when I have like 100 cs, even if those were only smaller creeps/minions, I should get at least 300 HP, but in one of my more recent games I had only around 150 HP (thats what the tooltip showed atleast. That didnt even include the kills i had... I have tried reproducing the error but it seems like its always a different amount of health u get. Sometimes even too much =D

I hope this helps to fix this bug.

Thx in advance!