I don't know if anyone else has noticed this before, but in random circumstances, when an NPC such as a necromancer or vampire casts a re-animation spell on a corpse, it glows as if it is being re-animated, but fails to stand up. I started noticing this after the official 1.9 patch came out. It still happens with the Unofficial Patches installed too.
Here is a screenshot that shows an example of this.
Here is another screenshot that shows an example of this.