has_and_belongs_to_many association with scope not joining correct table in scope.

rails_error.rb

unless File.exists?('Gemfile')
  File.write('Gemfile', <<-GEMFILE)
    source 'https://rubygems.org'
    gem 'rails', github: 'rails/rails'
    gem 'sqlite3'
  GEMFILE

  system 'bundle'
end

require 'bundler'
Bundler.setup(:default)

require 'active_record'
require 'minitest/autorun'
require 'logger'
 
# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)
 
ActiveRecord::Schema.define do
  create_table :students do |t|
  end
 
  create_table :groups do |t|
    t.integer :group_type_id
  end

  create_table :groups_students, :id => false do |t|
    t.integer :group_id,   :null => false
    t.integer :student_id, :null => false
  end

  create_table :group_types do |t|
    t.string  :name
  end
end
 
class Student < ActiveRecord::Base
  has_and_belongs_to_many :groups
  has_and_belongs_to_many :tutor_groups, -> { merge(Group.filter_type(:tutor_group)) }, class_name: "Group", join_table: "groups_students"
  has_and_belongs_to_many :tutor_groups2, -> { joins(:group_type).where(group_type: { name: :tutor_group }) }
end
 
class Group < ActiveRecord::Base
  has_and_belongs_to_many :students
  belongs_to :group_type

  def self.filter_type(type)
    joins(:group_type).where(group_types: { name: type })
  end
end

class GroupType < ActiveRecord::Base
  has_many :groups
end
 
class BugTest < Minitest::Test
  def test_association
    gt = GroupType.create(name: :tutor_group)

    g = Group.create
    g.group_type = gt
    g.save!

    s = Student.create
    s.groups << g
    s.save!

    query = Student.includes(:tutor_groups).first
  end
end