Proposed resolution:

This wording is relative to N5014.

1. Modify [format.tuple] as indicated:

   -1- For each of `pair` and `tuple`, the library provides the following formatter specialization where pair-or-tuple is the name of the template:

   namespace std {
     […]
     
     template<class... Ts> 
       constexpr bool enable_nonlocking_formatter_optimization<pair-or-tuple<Ts...>> = 
         (enable_nonlocking_formatter_optimization<remove_cvref_t<Ts>> && ...);
   }
   

The `enable_nonlocking_formatter_optimization` variable template is specialized only for cv-unqualified types. However, the specialization for `pair` and `tuple` does not remove the references and cv-qualifiers from the elements:

template<class... Ts> 
  constexpr bool enable_nonlocking_formatter_optimization<pair-or-tuple<Ts...>> = 
    (enable_nonlocking_formatter_optimization<Ts> && ...);

As consequence pair<const std::string, int> or pair<const std::string&, int&> (`map` and `flat_map` reference types) will not use unbuffered prints.

The proposed wording has recently been implemented in gcc's libstdc++.