Wrong damage calculation for Two-handed maces dual wielding

Hi,

I have finally reached the requirement needed for the giant's blood keystone in the warrior passive skill tree. However, my sunder and hammer of the gods damage are halved when I equip both two-handed maces and there is nothing in the tooltip indicating how the damage is calculated for dual wielding.
Also, it doesn't seem normal to me at all how ALL this setup REDUCES my damage by HALF. I think there must be something wrong with the calculations or at least something that is not written in the Sunder and Hammer of Gods tooltip.

I included two screenshots with the highest damage being with only the strongest mace and the lowest damage being with both maces.