Why does LD_PRELOAD not seem to work for write with wc

I was playing around with LD_PRELOAD to intercept libc calls, it appears that the write call doesn't get intercepted with wc, though it does seem to work with cat. A stripped down version of the problem appears below.

RedHat Linux 2.6.9-42.ELsmp

Makefile

writelib:
        gcc -Wall -rdynamic -fPIC -c write.c
        gcc -shared -Wl,-soname,libwrite.so -Wl,-export-dynamic -o libwrite.so write.o -ldl

write.c:

#include <stdio.h>
#include <string.h>
#ifndef __USE_GNU
 #define __USE_GNU
 #define __USE_GNU_DEFINED
#endif
#include <dlfcn.h>
#ifdef __USE_GNU_DEFINED
 #undef __USE_GNU
 #undef __USE_GNU_DEFINED
#endif
#include <unistd.h>
#include <stdlib.h>

static ssize_t (*libc_write)(int fd, const void *buf, size_t len);

ssize_t
write(int fd, const void *buf, size_t len)
{
    static int already;
    ssize_t ret;

    if (!already) {
            if ((libc_write = dlsym(RTLD_NEXT, "write")) == NULL) {
                    exit(1);
            }
            already = 1;
    }


    ret = (*libc_write)(fd,"LD_PRELOAD\n",11);
    return len; // not ret so cat doesn't take forever
}

Output:

prompt: make
gcc -Wall -rdynamic -fPIC -c write.c
gcc -shared -Wl,-soname,libwrite.so -Wl,-export-dynamic -o libwrite.so write.o -ldl
prompt: LD_PRELOAD=./libwrite.so /bin/cat write.c
LD_PRELOAD
prompt: LD_PRELOAD=./libwrite.so /usr/bin/wc write.c
 32  70 572 write.c

Any explanations ?