Nested through associations: preloads from the default scope of a through model should not be included in the association scope. (We're already excluding includes.) Fixes #2834.

activerecord/lib/active_record/associations/through_association.rb

@@ -16,7 +16,7 @@ module ActiveRecord
           chain[1..-1].each do |reflection|
             scope = scope.merge(
               reflection.klass.scoped.with_default_scope.
-                except(:select, :create_with, :includes)
+                except(:select, :create_with, :includes, :preload)
             )
           end
           scope

activerecord/test/cases/associations/nested_through_associations_test.rb

@@ -356,6 +356,15 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
     assert_equal categories(:general), members(:groucho).club_category
   end
 
+  def test_has_one_through_has_one_through_with_belongs_to_source_reflection_with_default_scope_preload_on_the_through_model
+    prev_default_scope = Club.default_scopes
+    Club.default_scopes = [Club.preload(:category)]
+
+    assert_equal categories(:general), members(:groucho).club_category
+  ensure
+    Club.default_scopes = prev_default_scope
+  end
+
   def test_has_one_through_has_one_through_with_belongs_to_source_reflection_preload
     members = assert_queries(4) { Member.includes(:club_category).to_a.sort_by(&:id) }
     general = categories(:general)