Proposed resolution:

1. Change the synopsis in [refwrap] paragraph 1:

   namespace std {
     template <class T> class reference_wrapper
     {
     public :
       [...]
       // invocation
       template <class... ArgTypes>
       typename result_of<T&(ArgTypes&&...)>::type
       operator() (ArgTypes&&...) const;
     };
   }
   

2. Change the signature in [refwrap.invoke] before paragraph 1

   template <class... ArgTypes>
   typename result_of<T&(ArgTypes&&... )>::type
   operator()(ArgTypes&&... args) const;
   

   1 Returns: INVOKE(get(), std::forward<ArgTypes>(args)...). (20.8.2)