diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 10ecd068d3..419967b833 100755
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -1273,9 +1273,16 @@ module ActiveRecord
             if send(reflection.name).loaded? || reflection.options[:finder_sql]
               send(reflection.name).map(&:id)
             else
-              send(reflection.name).all(:select => "#{reflection.quoted_table_name}.#{reflection.klass.primary_key}").map(&:id)
+              if reflection.through_reflection && reflection.source_reflection.belongs_to?
+                through = reflection.through_reflection
+                primary_key = reflection.source_reflection.primary_key_name
+                send(through.name).all(:select => "DISTINCT #{through.quoted_table_name}.#{primary_key}").map!(&:"#{primary_key}")
+              else
+                send(reflection.name).all(:select => "#{reflection.quoted_table_name}.#{reflection.klass.primary_key}").map!(&:id)
+              end
             end
           end
+
         end
 
         def collection_accessor_methods(reflection, association_proxy_class, writer = true)
diff --git a/activerecord/test/cases/associations/has_many_through_associations_test.rb b/activerecord/test/cases/associations/has_many_through_associations_test.rb
index 7a4712d7c8..8529ff0285 100644
--- a/activerecord/test/cases/associations/has_many_through_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_through_associations_test.rb
@@ -243,8 +243,12 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     assert_equal 2, people(:michael).jobs.size
   end
 
-  def test_get_ids
-    assert_equal [posts(:welcome).id, posts(:authorless).id].sort, people(:michael).post_ids.sort
+  def test_get_ids_for_belongs_to_source
+    assert_sql(/DISTINCT/) { assert_equal [posts(:welcome).id, posts(:authorless).id].sort, people(:michael).post_ids.sort }
+  end
+
+  def test_get_ids_for_has_many_source
+    assert_equal [comments(:eager_other_comment1).id], authors(:mary).comment_ids
   end
 
   def test_get_ids_for_loaded_associations
diff --git a/activesupport/lib/active_support/core_ext/hash/deep_merge.rb b/activesupport/lib/active_support/core_ext/hash/deep_merge.rb
index b009be3d84..ffde34a741 100644
--- a/activesupport/lib/active_support/core_ext/hash/deep_merge.rb
+++ b/activesupport/lib/active_support/core_ext/hash/deep_merge.rb
@@ -4,7 +4,7 @@ class Hash
     merge(other_hash) do |key, oldval, newval|
       oldval = oldval.to_hash if oldval.respond_to?(:to_hash)
       newval = newval.to_hash if newval.respond_to?(:to_hash)
-      oldval.class.to_s == 'Hash' && newval.class.to_s == 'Hash' ? oldval.deep_merge(newval) : newval
+      oldval.is_a?( Hash ) && newval.is_a?( Hash ) ? oldval.deep_merge(newval) : newval
     end
   end
 
diff --git a/activesupport/lib/active_support/core_ext/hash/diff.rb b/activesupport/lib/active_support/core_ext/hash/diff.rb
index da98593458..b904f49fa8 100644
--- a/activesupport/lib/active_support/core_ext/hash/diff.rb
+++ b/activesupport/lib/active_support/core_ext/hash/diff.rb
@@ -8,6 +8,6 @@ class Hash
   #   {}.diff(1 => 2)               # => {1 => 2}
   #   {1 => 2, 3 => 4}.diff(1 => 2) # => {3 => 4}
   def diff(h2)
-    dup.delete_if { |k, v| h2[k] == v }.merge(h2.dup.delete_if { |k, v| has_key?(k) })
+    dup.delete_if { |k, v| h2[k] == v }.merge!(h2.dup.delete_if { |k, v| has_key?(k) })
   end
 end
diff --git a/activesupport/lib/active_support/core_ext/hash/reverse_merge.rb b/activesupport/lib/active_support/core_ext/hash/reverse_merge.rb
index ebfdcb2cf0..d7ebd5feef 100644
--- a/activesupport/lib/active_support/core_ext/hash/reverse_merge.rb
+++ b/activesupport/lib/active_support/core_ext/hash/reverse_merge.rb
@@ -21,7 +21,7 @@ class Hash
   # Performs the opposite of <tt>merge</tt>, with the keys and values from the first hash taking precedence over the second.
   # Modifies the receiver in place.
   def reverse_merge!(other_hash)
-    replace(reverse_merge(other_hash))
+    merge!( other_hash ){|k,o,n| o }
   end
 
   alias_method :reverse_update, :reverse_merge!
diff --git a/activesupport/lib/active_support/hash_with_indifferent_access.rb b/activesupport/lib/active_support/hash_with_indifferent_access.rb
index 61fc6475a0..543dab4a75 100644
--- a/activesupport/lib/active_support/hash_with_indifferent_access.rb
+++ b/activesupport/lib/active_support/hash_with_indifferent_access.rb
@@ -98,6 +98,10 @@ module ActiveSupport
       super other_hash.with_indifferent_access
     end
 
+    def reverse_merge!(other_hash)
+      replace(reverse_merge( other_hash ))
+    end
+
     # Removes a specified key from the hash.
     def delete(key)
       super(convert_key(key))
@@ -109,7 +113,7 @@ module ActiveSupport
 
     # Convert to a Hash with String keys.
     def to_hash
-      Hash.new(default).merge(self)
+      Hash.new(default).merge!(self)
     end
 
     protected