unscoped does not work when chained with named_scope

activerecord/lib/active_record/base.rb

@@ -876,6 +876,11 @@ def arel_engine
       #     limit(10) # Fires "SELECT * FROM posts LIMIT 10"
       #   }
       #
+      # It is recommended to use block form of unscoped because chaining unscoped with <tt>named_scope</tt>
+      # does not work. Assuming that <tt>published</tt> is a <tt>named_scope</tt> following two statements are same.
+      #
+      # Post.unscoped.published 
+      # Post.published 
       def unscoped
         block_given? ? relation.scoping { yield } : relation
       end