I am not sure if I understand this enhancement for Tiefling but it says in the description "Enemies affected by your Scorch spell increase Fire damage that they take by 5%. When cast on a creature that is immune to Fire, it makes them vulnerable to that element for a short period of time." So does making them vulnerable make them take damage afterwards because when I hit them with fire it still says immune and no damage? Is this a bug or am I not understanding the enhancement?