[1.80] combine Chrono library with c++0x, but use it with c++98

[youngwolf-project]

I built Boost without any specific customization, which is:
./bootstrap
./b2

Before 1.80, following codes can work properly (-std=c++98), but in 1.80, it must be compiled with -std=c++0x (or heigher) or with macro BOOST_CHRONO_HEADER_ONLY, otherwise, the timer can never expire. My query is -- is this a bug or right behavior by design?

void timer_handler(const boost::system::error_code& ec, const boost::shared_ptr<boost::asio::system_timer>&)
{
    puts("receive a timeout event.");
}
void main()
{
    boost::asio::io_context ctx[4];
    for (int i = 0; i < 16; ++i)
    {
        BOOST_AUTO(timer, boost::make_shared<boost::asio::system_timer>(ctx[i % 4].get_executor()));
        timer->expires_after(boost::chrono::milliseconds(50));
        timer->async_wait(boost::bind(&timer_handler, boost::asio::placeholders::error, timer));
    }
    boost::thread_group tg;
    for (int i = 0; i < 4; ++i)
        tg.create_thread(boost::bind(&boost::asio::io_context::run, &ctx[i]));
    tg.join_all();
}