Fatigue & Undead

[MaxWilson]

Apologies if this has been asked recently, but I searched and couldn't find it.

I thought undead, or any unit with zero encumbrance, was supposed to never accumulate fatigue except through spellcasting, no matter what armor they wear. I have a Wraith Lord who's fighting hordes of Jotun Militia while wearing Stone Boots (Stoneskin effect), a Pendant of Luck, and a Horror Helmet. He's scripted to <cast "Soul Vortex", Attack Closest>. This works fine except that every time he swings his sword he seems to pick up 13 or so fatigue, although after he gets surrounded by Jotuns he leeches it all back (which is in itself odd; since Life Leech does only 1 point of damage, I don't see how it's possible to leech more than 16 points of fatigue even if there are enemies on all 8 squares around you). Anyway, I don't understand where this 13 fatigue is coming from, since his encumbrance is zero. Can anybody help me understand?

Thanks,
Max Wilson