Eager Loading a HABTM with further includes does not properly load when duplicates are in the HABTM

When eager loading a HABTM and also including anything beyond it, duplicate objects in the HABTM only load the first object's further includes, but the further includes are not loaded for subsequent objects. It's hard to explain succinctly, so here's an example (with a test down further down):

Post has_and_belongs_to_many Categories and Categories has_many Categorizations.
Post 1 has categories 1 and 3.
Post 2 has category 1.
Calling Post.find(:all, :include => {:category => :categorizations}) will cause the categorizations to be loaded for the category objects tied to Post 1, however the category object for Post 2 will not have the categorizations loaded. Subsequent calls to it will show database queries executing.

From what I can tell...In preload_associations, after the first level :category include is handled, it passes an array of categories [1, 3, 1] to the next level of preload_associations for the :categorizations. preload_associations calls uniq right at the start on the records passed in. The uniq ends up changing it to [1, 3], and that is how the duplicates are lost. If I remove the uniq call, the test below passes, however then it breaks test_including_duplicate_objects_from_belongs_to. Since that uniq call is in AR 2.2+, I am assuming this will happen on all versions including 3.

Add the following test to cases\associations\eager_test.rb, and also add a require for 'models\categorization' and the fixture for :categorizations (patch attached, but it's against 2.2.2).

  def test_deep_including_through_habtm
    posts = Post.find(:all, :include => {:categories => :categorizations}, :order => "posts.id")
    assert_no_queries { assert_equal 2, posts[0].categories[0].categorizations.size }
    assert_no_queries { assert_equal 0, posts[0].categories[1].categorizations.size }
    assert_no_queries { assert_equal 2, posts[1].categories[0].categorizations.size }
  end

The third assert_no_queries will fail. If you change the very first line of preload_associations to remove the uniq, the test will pass, however test_including_duplicate_objects_from_belongs_to will fail. For now, that's the only way I could get the test to pass.