Sacrifice bug?

[Sigma88]

I know that some units cannot be fodder for Sacrifice, such as summoned monsters/creatures. However I do know that you can target units such as hypnotized or charmed enemies. I'm using a demoness to charm enemies and have been doing them for quite a while now. But sometimes i cannot target some charmed enemies despite me being able to just a few rounds ago.

What's up with that? I don't think hp was a factor, i may get less back but i've been able to kill the entire units this way.