the zombie trait is the one that makes you take damage from healing and heal from poison and was always in the game... which is now forced on undead as a baseline trait...
but you also forgot the part where undead are immune to bleeding as well.
Ah so that all grouped up is actually called "zombie trait" o well my mistake
PS but there is nooooo way zero logic to make skeletons bleed.... I mean how on earth to do that maybe extra soft on maces but skeleton and bleed??? from where???