Trusted Kinship keystone bug

it seems that the Trusted Kinship keystone is applying a damage taken increase on top of the 30% defences reduction.
The difference between having the Keystone and using Yriel Fostering is night and day, even with my defences being overall lower using Yriels Fostering.
I cant explain it other than there's an additional damage taken increase happening under the hood with the keystone