Noticing this with my Breton today, but the CP Magicka Attribute Bonus is Multiplicative with other % bonuses such as the breton racial and the Ancient Grace Set. However, the Breton Racial and Ancient Grace set are additive with one another. Not sure if that is intended.
Most of the multiplicative vs additive mechanics have been screwed since morrowind, executes are broken, so is hardy and ed (order of cp choices change if its multiplicative or additive).