ToME: the Tales of Maj'Eyal

A lua error message each time an enemy of rare [pink text] rarity activates any talent, when its on screen. The error message from the log below:
Lua Error: /mod/class/interface/ActorAI.lua:1599: attempt to perform arithmetic on local 'status_chance' (a nil value)
At [C]:-1 __sub
At /mod/class/interface/ActorAI.lua:1599 aiTalentTactics
At /mod/ai//improved_tactical.lua:590
At /mod/class/interface/ActorAI.lua:70 runAI
At /mod/ai//improved_tactical.lua:1139
At /mod/class/interface/ActorAI.lua:70 doAI
At /mod/class/NPC.lua:77 act
At /engine/GameEnergyBased.lua:129 tickLevel
At /engine/GameEnergyBased.lua:64 tick
At /engine/GameTurnBased.lua:51 tick
At /mod/class/Game.lua:1519
---------------- Stack Dump ----------------
--------------- Stack Dump Finished ---------------

Many stacks, the same message, probably on every talent activation "tick". Doesn't activate when the enemy simply attacks, even when sustaining a talent (only the sustain activation gives an error).