Is this a bug in implementation of std::format_to_n in g++ 13.2?

Consider the following snippet:

// #define USE_FMTLIB

#include <chrono>
#include <iostream>

#if defined(USE_FMTLIB)
    #include <fmt/chrono.h>
    #include <fmt/core.h>
#else
    #include <format>
#endif


int main() {
    constexpr std::size_t STATIC_BUFF_SIZE = 1024;
    static char static_buff[STATIC_BUFF_SIZE];

    const auto timepoint = std::chrono::system_clock::now();
    const auto prefix_format_result = 
#if defined(USE_FMTLIB)
        fmt::format_to_n(
#else
        std::format_to_n(
#endif    
            static_buff, STATIC_BUFF_SIZE,
            "timestamp:{:%Y-%m-%d %H:%M:%S}",
            timepoint
    );
    std::cout << (prefix_format_result.out - static_buff) << "\n";
}

(compilers keys are the default ones for g++ in compiler explorer: -std=c++20 -O3 -Wall -Wextra -pedantic -pedantic-errors).

When USE_FMTLIB is enabled (original fmt is used for formatting) the code outputs 39. Otherwise, it outputs 1024 for g++ 13.2; for 13.3, 14.1, 14.2 and forth it outputs 39 (sometimes in compiler explorer compilation fails due to timeout).

1. So, it looks like a bug in g++13.2, or sth wrong with this code?
2. In both fmt and std, format_to_n returns struct containing two fields: size and out. Aren't they duplicate each other? I mean, if we know size (the number of symbols written to buffer during formatting), we easily could compute out (as I understand, it is pointer/iterator to position after formatted sequence) and vice versa.

1. std::format_to_n_result

   Notes

   The libstdc++ implementation prior to GCC-13.3 had a bug in reporting the correct format_to_n_result::out value.

2. No, they don't duplicate each other. size can be greater than n if the output result is truncated.