Proposed resolution:

This wording is relative to N4800.

1. Change class template istreambuf_iterator synopsis, [istreambuf.iterator], as indicated:

   template<class charT, class traits = char_traits<charT>>
   class istreambuf_iterator {
   public:
     using iterator_category = input_iterator_tag;
     using value_type        = charT;
     using difference_type   = typename traits::off_type;
     using pointer           = voidunspecified;
     using reference         = charT;
     […]
   };