select_on_container_copy_construction not called for std::string

select_on_container_copy_construction in my allocator is not called for std:::string. It works fine when used with a vector tough. Why is the behavior different? Is this a bug in GCC?

Code example with a minimal allocator:

#include <iostream>
#include <vector>

template<class T>
class allocator {
public:
  typedef T value_type;

  using propagate_on_container_copy_assignment = std::true_type; // for consistency
  using propagate_on_container_move_assignment = std::true_type; // to avoid the pessimization
  using propagate_on_container_swap = std::true_type; // to avoid the undefined behavior

  allocator<T> select_on_container_copy_construction() const {
    std::cout << "COPY THROW!!!" << std::endl;
    throw std::bad_alloc();
  }

  T *allocate(const std::size_t n) {
    return static_cast<T *>(::operator new(n * sizeof(T)));
  }

  void deallocate(T *, const std::size_t) {
    /*no op*/
  }
};

int main()
{
  std::basic_string<char, std::char_traits<char>, allocator<char>> s;
  auto ss = s; // Does not output anything, select_on_container_copy_construction NOT called.

  std::vector<int, allocator<int>> v;
  auto vv = v; // Correctly calls select_on_container_copy_construction and exits.

  return 0;
}