It's not the death. It's the specific vengeance mechanic. When a dwarf sees another dwarf in combat, he generally decides to join in. And when he joins the fight, he has a chance to take a lump of stress as vengeance.
This creates a funny problem in a reanimating biome. Suppose that forty dwarves are looting the corpses of a defeated elf army. Suddenly, the severed head of an elf bowman reanimates and starts trying to bite someone. It's no threat to anyone, but it starts a combat with the nearest dwarf. If that combat lasts more than a few ticks, then all forty dwarves decide to join in, which means that they all have a chance to add stress for vengeance. It only takes a few seconds for the nearest dwarves to kill the reanimated head, and all the nearby dwarves drop out of combat mode and resume looting.
Multiply that scene by number of heads, arms, and non-mangled corpses in a defeated elf army, and those dwarves could take 20 to 50 vegeance hits to stress before all the elf parts are dumped and smashed.
This is probably working as intended. It makes sense that battling the dead would be as much a psychological challenge as a martial one. So I've learned to plan around the vengeance mechanic and make sure that my dwarves aren't overly concentrated around corpses or body parts that are likely to reanimate. And I don't know if this has been altered in 44.10.