[PATCH] Eager loading don't work properly on nested includes

If we have a following models:

class Article < ActiveRecord::Base
  has_and_belongs_to_many :tags
end

class Tag < ActiveRecord::Base
  has_and_belongs_to_many :articles
  has_many :translations
end

class Translation < ActiveRecord::Base
  belongs_to :tag
end

and some seed data:

tag1_translation = Translation.create!
tag2_translation = Translation.create!
tag3_translation = Translation.create!
tag4_translation = Translation.create!
tag1 = Tag.create! :translations => [tag1_translation]
tag2 = Tag.create! :translations => [tag2_translation]
tag3 = Tag.create! :translations => [tag3_translation]
tag4 = Tag.create! :translations => [tag4_translation]
article1 = Article.create! :tags => [tag1, tag2]
article2 = Article.create! :tags => [tag2, tag3]
article3 = Article.create! :tags => [tag1, tag2, tag3]
article4 = Article.create! :tags => [tag4]

Then this query:

Article.includes(:tags => :translations)

will not preload :translations to all tag objects

 > Article.includes(:tags => :translations).map { |a| a.tags.first.id }
=> [1, 1, 1, 4] 
 > Article.includes(:tags => :translations).map { |a| a.tags.first }.map(&:translations).map(&:loaded?)
=> [true, false, false, true]

The bug appears when we have one record mapped into several ruby objects - then only one object of those will get next "includes()".

After some investigations, I've come to this line:
https://github.com/rails/rails/blob/master/activerecord/lib/active_...

If I remove ".uniq" call - everything works just fine except one failing test - test_including_duplicate_objects_from_belongs_to.