They should be using their Poison Claw attack above 50% HP. Let me run some tests to see if that's not set up right.
EDIT: There were quite a few AI issues that I'm about to resolve in a second round of patching. (Also, a certain lategame enemy needs a BIT less magic power, so I'm doing something about that too, especially to make up for the fact that the enemies will be much less stupid.)