hitting energy shield with only chaos damage dealt

using replica alberon's warpath boots, which have the line cannot deal non-chaos damage, meaning i should always bypass energy shield, with molten strike of the zenith i am seeing boss enemies shield go down in big chunks, about 1/3rd of the bar, very rarely, but for instance i've gotten searing exarch shield to 10% in 2 hits.

i am unsure if this is a bug with the new boss hp bars, as the hits are seemingly big single hits which i do a bunch of mostly small hits so if it was letting my damage through into the shield wouldn't add up.

i am unsure how to reproduce the bug, but just using ms of the zenith with alberons warpath and a flat chaos damage 2h sword should be all the conditions, otherwise check my character Brogset for tree/gearing if unable to reproduce.