Problem:
We can create invisible file in ZFS.
How to reproduce:
0. Prepare normalization formD ZFS.
    # cat cat /etc/release
    cat: cat: No such file or directory
                 OpenIndiana Development oi_151 X86 (powered by illumos)
            Copyright 2011 Oracle and/or its affiliates. All rights reserved.
                            Use is subject to license terms.
                               Assembled 28 April 2011
    # mkfile 100M 100M
    # zpool create -O utf8only=on -O normalization=formD test_pool $( pwd )/
100M
    # zpool upgrade
    This system is currently running ZFS pool version 28.

    All pools are formatted using this version.
    # zfs get normalization test_pool
    NAME       PROPERTY       VALUE          SOURCE
    test_pool  normalization  formD          -
    # chmod 777 /test_pool

1. Create a NFD file.
    $ cd /test_pool/
    $ cp /etc/release $( echo "\x75\xcc\x88" )
    $ ls -la
    total 4
    drwxrwxrwx  2 root  root    3 2011-07-29 08:53 .
    drwxr-xr-x 25 root  root   26 2011-07-29 08:53 ..
    -r--r--r--  1 test1 staff 251 2011-07-29 08:53 u?