Child bonus broken?

[Iggy]

Foolstone, that's my exact problem. Example:

+1 def from Warrior Helmet (on the wife)
+2 def from Horned Helmet.
+3 def from Scaly Armor
+3 def from Kerian Shoes
+2 def from Guard's Shield
+2 def from Steel Belt
+2 def from 2 Altars of Combat


Which adds up to exactly 15. No 20% bonus to defense anywhere, otherwise the final defense score would be 18. I don't think poor translation is an issue in this case.