Linux setrlimit() doesn't kill process

Question

From man page of setrlimit, when RLIMIT_CPU limit is set, process should receive SIGXCPU every second once the soft limit is reached, and SIGKILL when the hard limit is reached.

I have the following code where the child process is created using clone() call. Then RLIMIT_CPU is set followed by long loop, which should be terminated via SIGKILL. This seems to work with SIGCHLD flag set. However, when I use SIGCHLD | CLONE_NEWPID flags, the loop doesn't terminate.

EDIT:

What happens on my machine: program writes pid 1 interrupted two times, and then execution freezes (loop is running and isn't killed) until loop is finished. This lasts about 10 seconds. When I remove CLONE_NEWPID program terminates after 3 seconds.

#define _GNU_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <signal.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/wait.h>
#include <unistd.h>
#include <sched.h>

int inside(void *arg)
{
    struct rlimit r = {1, 3};
    setrlimit(RLIMIT_CPU, &r);
    for (long long i = 0; i < 3e9; i++);
    return 0;
}

void handler(int signal)
{
    printf("pid %d interrupted\n", getpid());
    fflush(stdout);
}

void setup_signals(void)
{
    struct sigaction s;
    bzero(&s, sizeof s);
    s.sa_handler = handler;
    sigaction(SIGXCPU, &s, NULL);
}

int main(void)
{
    const int stack_size = 1 << 16;
    char stack[stack_size];
    setup_signals();
    int pid = clone(inside, stack + stack_size, SIGCHLD | CLONE_NEWPID, NULL);
    if (pid < 0) return 1;
    wait(NULL);
    return 0;
}

Why the child process is not killed (it gets killed if you remove CLONE_NEWPID)?