[Gameplay] Zac Takes True Damage During Passive bug

yo. so a friend of mine plays a lot of Zac (one of the few who do) and he noticed the other night that after checking his death recap there was a support Thresh who did like 1600 true damage via AA, so naturally we were like wtf. after we paid closer attn to it we noticed that all dmg Zac receives (turret, phys, mgc, AA, minion hits etc) is true damage to his blobs. this happens every single time.

below i shall include some screenshots via gallery from a custom bot game i did not 10 mins ago. ( sry i'd have more but i do not have the patience to do it again and again )

http://imgur.com/a/TEreO

bug or what? pls n ty Rito.