I'm seeing this behavior in mongoid 3 when using eager loading with default scopes. I'm not sure if it's a bug or by design.

Simple example:

class Person
  include Mongoid::Document
  field :name
  has_many :hobbies
end

class Hobby
  include Mongoid::Document
  field :name
  field :status
  belongs_to :person
  default_scope where(:status.ne => 'deleted')
end

After creating a person and two hobbies, one of them with status = 'deleted', person = Person.includes(:hobbies).first correctly performs the eager load query (including the default scope), but then person.hobbies hits the database again. Removing the default scope causes it to work as expected.