[GAMEPLAY] Zz'Rot Portal Voidlings gain no bonus damage

I played a match as Thresh, my build consisting of Talisman of Ascension, Merc Treads, Ruby Sightstone, Randuin's Omen, Banshee's Veil and Zz'Rot Portal as the last item. Although I had lots of resistencies, the Zz'rot Portal Tooltip would state that the voidlings would gain no bonus damage, meaning the number in brackets was 0. I did not check in depth if it is simply a tooltip bug or if the voidlings really are bugged, but I do think that the latter is the case.