Heroes 6 - Discussion

I'm playing through the Haven campaign with a mage hero. Even on the second map, the cost of spells has increased by a third, just like in the Necropolis and Sanctuary campaigns. I understand that this is part of the game mechanics – to increase the cost of spells as mana increases, to avoid imbalance in favor of mages. But on the third map, all Light magic spells have become several times more expensive. Healing now costs 128 mana, and the second-level Tears of Repentance skill costs 510, even with a full mana pool, it's impossible to use. Has anyone else encountered this?