I noticed that one of my characters had managed to reach a 150+ health regeneration stat recently, and it seems that this is due to a profuse use of the "Deathly Hex" spell, which applies a debuff to your character (-1 health regeneration for 6 turns, -1 max health for 90 turns). If I gained a level while this debuff was in effect, the game reset my max health and health regeneration as if the debuffs were not active. Then, when the debuffs expired after leveling, the stats increased beyond that. For example, if I cast the spell 50 times, then leveled up, my max health would increase by 50 units more than it should have. I also tested this with the nightmare curse, and would assume that this happens for all debuffs that affect your character's stats. I wouldn't be surprised if it also occurs on positive effects, but I haven't tested that.
