Don't merge just directly add to the action to the :partial key

actionpack/lib/abstract_controller/rendering.rb

@@ -144,7 +144,7 @@ def _normalize_args(action=nil, options={})
         key = action.include?(?/) ? :file : :action
         options[key] = action
       else
-        options.merge!(:partial => action)
+        options[:partial] = action
       end
 
       options