nerdook: They do attack, but they have to be coming from behind an enemy for this to be noticeable. If they bump into an enemy head on, their health is so low that they'll most likely get destroyed before they can get any hits in. But then, you have a LOT of them!
I tried the Necromancer trait again and got to level 8. I watched closly, but still, none of the skeletons did damage to any of the enemies. If this is really their attack pattern, only from behind, I can see why, because they move so slowly compared to the enemies that they (probably) can never get effectively behind one of them. Maybe, if you have a big group of skeletons, like from the Raise Dead skill, where the skeletons do noticeable damage, this works. But with Necromancer I never got more than two skeletons on the same platform with an enemy.
So it's not a bug, but by itself the Necromancer trait seems pretty worthless. But I will try a combination of Necromancer and Raise Dead, if I get the chance.
Still, it's a fantastic game, and I've already put several hours into it. By the way, how do I access New Game+? I've beaten the game twice now, and it says I've unlocked New Game+, but by the holy contortions of my brain, I can't find how to access this mode.