Possible AR Polymorphic Association Regression (5.2.0.beta2)?

issue.rb

# frozen_string_literal: true
# https://raw.githubusercontent.com/rails/rails/master/guides/bug_report_templates/active_record_master.rb

gem "bundler", "< 1.16"

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem "rails", github: "rails/rails"
  #gem 'rails', '~> 5.2.0.beta2'
  #gem "sqlite3"
  gem "pg"
end

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.establish_connection("postgresql://localhost/arpoly?pool=3")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  enable_extension 'uuid-ossp'
  enable_extension 'pgcrypto'
  create_table :posts, id: :uuid, force: true do |t|
    t.timestamps null:false
  end

  create_table :trackers, force: true do |t|
    t.string   :track_type  , null:false
    t.uuid     :track_id    , null:false
    t.timestamps null:false
  end
end

class Post < ActiveRecord::Base
  has_one    :tracker, as: :track
end

class Tracker < ActiveRecord::Base
  belongs_to :track, polymorphic:true
end

class BugTest < Minitest::Test
  def test_association_stuff
    post = Post.create
    Tracker.create(track:post)
    tracker = Tracker.first
    p tracker
    post = tracker.track
    p post

    assert_equal tracker.track_id, post.id

    #assert_equal 1, post.comments.count
    #assert_equal 1, Comment.count
    #assert_equal post.id, Comment.first.post.id
  end
end