The new libpthread records the pthread_exit_process() exit handler with
cxa_atexit() instead of on_exit() when possible.
The glibc exit() does not include the exit code when calling this flavor 
of exit handler.
As a side effect, a multithreaded program will always terminate with the
exit code 0 if the thread that does exit() is not the main thread.

Ludo.

How to reproduce
-----------------
$ cat test.c
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

void*
do_exit(void* dummy)
{
    /*
     * Just call exit with code 2.
     */
    printf("exit thread does exit\n");
    exit(2);
}


main()
{
    int       ret;
    pthread_t th_exit;

    /*
     * Create a default pthread to handle the 
     * process exit.
     */
    ret = pthread_create(&th_exit, NULL, do_exit, NULL);
    if (ret != 0) {
	perror("pthread_create failed");
	exit(1);
    }
    /*
     * Just loop indefinitely waiting for the
     * process to exit.
     */
    printf("main thread loops\n");
    while(1);
    /*
     * NEVER REACHED
     */
    return 0;
}

$./test; echo $?
0 <- Should actually be 2