We're seeing the following unusual behavior of the program below on Red Hat
Advanced Server 4, Update 4:

$ cat t.c && gcc t.c && rm -f foo.out && ./a.out > foo.out && ls -l foo.out &&
du -k foo.out
#include <stdio.h>
#include <wchar.h>

int main ()
{
    puts ("");
    ungetwc ('A', stdout);
    fwide (stdout, 0);
    return 0;
}
-rw-r--r--  1 sebor devel 182888783729 May 24 16:44 foo.out
16      foo.out

The output of strace on the program is in the attached file.

Here's info on libc:

$ ldd a.out && /lib64/tls/libc.so.6
        libc.so.6 => /lib64/tls/libc.so.6 (0x000000381b500000)
        /lib64/ld-linux-x86-64.so.2 (0x000000381b100000)
GNU C Library stable release version 2.3.4, by Roland McGrath et al.
Copyright (C) 2005 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 3.4.6 20060404 (Red Hat 3.4.6-2).
Compiled on a Linux 2.4.20 system on 2006-07-04.
Available extensions:
        GNU libio by Per Bothner
        crypt add-on version 2.1 by Michael Glad and others
        Native POSIX Threads Library by Ulrich Drepper et al
        RT using linux kernel aio
        The C stubs add-on version 2.1.2.
        GNU Libidn by Simon Josefsson
        BIND-8.2.3-T5B
        NIS(YP)/NIS+ NSS modules 0.19 by Thorsten Kukuk
Thread-local storage support included.
For bug reporting instructions, please see:
<http://www.gnu.org/software/libc/bugs.html>.