[SolAndLuna]

Again, fairly simple one this time - The Coastal Squall (and presumably, other tomes like it) amplifies damage done with certain elements. While it does do so correctly with usual spells, like Evoker or Aquamancer, it doesn't seem to work at all in the case of youkai evokes.

Given that the exact wording on the tome's description is "+UL% Power to Aquarian Spells (Halved if not main weapon.);+UL% Power to Sylphid Spells (Halved if not main weapon.)", this doesn't seem like an intentional function of the tome, seeing as there is no other conditional in the description.