Removing association with dependent: :destroy, through nested attributes leaves entity from intermediate table in memory

[pn-y]

Steps to reproduce

# frozen_string_literal: true

require 'bundler/inline'

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

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

  gem "activerecord", '~> 6'
  gem 'sqlite3'
end

require 'active_record'
require 'minitest/autorun'
require 'logger'

ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :users, force: true do |t|
  end

  create_table :user_pings, force: true do |t|
    t.integer :user_id
    t.integer :ping_id
  end

  create_table :pings, force: true do |t|
  end
end

class User < ActiveRecord::Base
  has_many :user_pings, inverse_of: :user
  has_many :pings, through: :user_pings, inverse_of: :users

  accepts_nested_attributes_for :user_pings, allow_destroy: true
end

class UserPing < ActiveRecord::Base
  belongs_to :user, inverse_of: :user_pings
  belongs_to :ping, inverse_of: :user_pings
  accepts_nested_attributes_for :ping, allow_destroy: true
end

class Ping < ActiveRecord::Base
  has_many :user_pings, dependent: :destroy, inverse_of: :ping
  has_many :users, through: :user_pings, inverse_of: :pings
end

class AssociationTest < Minitest::Test
  def setup
    user = User.create
    user.pings.create
  end

  def test_association
    user = User.first
    user_ping = UserPing.first
    ping = Ping.first

    user.update(user_pings_attributes: [{ id: user_ping.id, ping_attributes: { id: ping.id, _destroy: true } } ])

    assert(user.pings.length == 0)
    assert(user.user_pings.length == 0)
  end
end

Last assert will fail.

Expected behavior

Both associations should be blank without user.reload

Actual behavior

Association from through table still available on user object

System configuration

Rails version: 5.2.3

Ruby version: ruby 2.5.1p57

[rails-bot]

This issue has been automatically marked as stale because it has not been commented on for at least three months.
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