spell book reuse won't burn or poison

[exxo]

Hi guys, new to the forum.

I am having difficulty in finding an answer to my question online, so here it goes.

I am a level 7 mage and right after i activated the higher magic 1 which allowed me to use the spell book 2 times I observed that my poison and magic arrow won't cause any poison/burning which used to last 2/3 turns after impact. I have tried this on a number of opponents from pirates, orcs, mages, etc.

Why is that? Is it a bug or I don't have enough intellect or something?

Thank you for your help.