to_sentence should return a duplicate

activesupport/lib/active_support/core_ext/array/conversions.rb

@@ -26,7 +26,7 @@ def to_sentence(options = {})
       when 0
         ""
       when 1
-        self[0].to_s
+        self[0].to_s.dup
       when 2
         "#{self[0]}#{options[:two_words_connector]}#{self[1]}"
       else

activesupport/test/core_ext/array_ext_test.rb

@@ -82,6 +82,11 @@ def test_one_element
     assert_equal "one", ['one'].to_sentence
   end
 
+  def test_one_element_not_same_object
+    elements = ["one"]
+    assert_not_equal elements[0].object_id, elements.to_sentence.object_id
+  end
+
   def test_one_non_string_element
     assert_equal '1', [1].to_sentence
   end