I've noticed many times when enemies cast a spell that has a pip cost (specially happened with natural attacks, spells with X pip cost, and high pip cost spells) their pips won't consume till beginning of next round.
I have also noticed that any spell that has a X cost is not sorted correctly in the spell book. For example: Judgement appears after Sap Health which is a Rank 1 and Tempest appears after windstorm which is also a Rank 1. There maybe a bug with the way the spells are sorted which may be linked to how the graphics bug. This is currently happening with Tempest , Judgement, and Heck Hound based on observation.