bizarre blood hunt results

[Ygorl]

I've been experimenting with hunting for blood slaves in my capital, as Mictlan. Sometimes, though, I lose my scales! In particular, heat and/or growth disappear. This tends to happen within the first couple turns of the game; only those two ever disappear, sometimes just one of them. I can get them back by working my dominion all the way up to maximum and then waiting for a while, but I don't see any reason why this would happen at all. It only happens when I'm bloodhunting, and then only sometimes. There's no event associated with it. It stinks, because the lost money really is useful early in the game... Can anyone explain this, or is it a bug?