Polymorphic association doesn't use model_name

I have the following (simplified) setup:

class User < ActiveRecord::Base;
class Member < ActiveRecord::Base;

class MemberResource < JSONAPI::Resource
  model_name 'User'
end

class BookResource < JSONAPI::Resource
   has_one :author, polymorphic: true  # type is 'Member' here
end

class AuthorResource < JSONAPI::Resource; end

When I tried to request GET /books/:book_id/author JR will load Member from members table and not users as it's described with model_name.

Would say it's a bug?

I know that my use case is a little bit complex, but in that simplified example we decide to show User as Member in the API (we have different model names).

Start by tracing the GET /books/:book_id/author path for BookResource's polymorphic author association and compare its type resolution with MemberResource's model_name 'User'. Reproduce the example with User, Member, MemberResource, and BookResource, then verify that the association resolves to users rather than members while preserving the API resource names.