Evil Eye "Drain Life" ability question

[Sertorius]

First, let me say that the added Beholder troops are probably my favorite addition to any of the KB games. I love love love the Evil Eye, even though his is grossly overpowered. I want a full roster of Beholders but can't find the regular Dark Beholders from the previous iterations of the series yet. Soon!

But the question: the Evil Eye's "Drain Life" (or "Vampirism") ability does not seem to work, whether with his ranged lightning attack *or* in direct melee. Am I missing something or is it bugged?

Also can I say that the search function on this forum is an absolute nightmare? Sorry if an answer to this has been posted already.