ruby-on-rails - Different behaviour of self referential model. Is it a bug?

Question

It seems that I found a bug. I have two similar models that behave differently.

I have a Post model that belongs_to an Author.

I have a Task model that is self-referencing.

Model code:

app/models/author.rb:

class Author < ActiveRecord::Base
  has_many :posts
end

app/models/post.rb:

class Post < ActiveRecord::Base
  belongs_to :author

   scope :published, -> { where(status: 1) }

   after_create do
     puts '========================================='
     puts "author_id is present: '#{author_id}'"
     puts "what about task association? '#{author}'"
     puts '========================================='
   end
end

app/models/task.rb:

class Task < ActiveRecord::Base
  belongs_to :task
  has_many :tasks

  scope :published, -> { where(status: 1) }

  after_create do
    puts '========================================='
    puts "task_id is present: '#{task_id}'"
    puts "what about task association? '#{task}'"
    puts '========================================='
  end
end

Both Post and Task are similarly scoped, but behave differently:

Author.create.posts.published.create    # works

Task.create.tasks.published.create      # doesn't work

Task.create.tasks.create                # works

There is an after_create callback in Task model, where it should print the parent Task but it is nil despite task_id having the correct ID of parent.

Why is it behaving differently?