Checked in a speculative fix for this. I think the reason it was breaking is that for some reason, the creatures in question were only spawning once, then not respawning after they were killed. It looks like it's working now, but then, it did before too (because apparently lizardmen aren't very good at doing what I ask).
Let me know if you're still seeing this again tomorrow.
Actually, you know what? I can just check now. I'm going to finish what I'm working on real fast, then hop in and test it. HOORAY FOR LIVE TOOLS! HOORAY FOR STREAM OF CONSCIOUSNESS THINKING ON FORUM POSTS!