Feldoth noticed that Divine Illumination (our new 41st talent in the Holy tree) could possibly be overpowered in combination with Illumination. Why? Because Divine Illumination halfs the mana cost of all spells, whereas Illumination gives the base mana cost back per every heal you crit. So in essence, you can gain mana while healing if you have an high enough spell crit. Cool, eh? The big question is whether this was intended or not.