compilation fails on unordered_flat_map with certain key , value

[kantan2015]

unordered_flat_map::try_emplace fails to compile with certain key, value type. Key : boost::flyweight Value: std::vector with move only type

version: gcc13.2, boost 1.85

#include <unordered_map>
#include <boost/unordered/unordered_map.hpp>
#include <boost/unordered/unordered_flat_map.hpp>
#include <string>
#include <boost/flyweight.hpp>

template<class Map, class Key> 
void try_emplace(Key key) {
    Map map;
    map.try_emplace(key);
} 

using move_only_vec = std::vector<std::unique_ptr<int>>;
 try_emplace<boost::unordered_flat_map<int, move_only_vec>>(1);   // ok

 boost::flyweight<std::string> s("1"); 
 try_emplace<std::unordered_map<boost::flyweight<std::string>, move_only_vec>>(s); // ok
 try_emplace<boost::unordered_map<boost::flyweight<std::string>, move_only_vec>>(s); // ok  
 //try_emplace<boost::unordered_flat_map<boost::flyweight<std::string>, move_only_vec>>(s); // ng   
 try_emplace<boost::unordered_flat_map<boost::flyweight<std::string>, std::unique_ptr<int>>>(s); // ok