Unable to delete a user from a Linux CentOS 6.3 machine, what can be done?

When I try deleting my user (from a root shell) it says userdel: cannot remove entry 'itaig' from /etc/passwd The user isn't even displayed on /etc/passwd.

[root@ab2c1 ~]# su - itaig
su: warning: cannot change directory to /home/itaig: No such file or directory
-bash-4.1$ exit
logout
[root@ab2c1 ~]# mkdir /home/itaig
[root@ab2c1 ~]# chown itaig.itaig /home/itaig/
[root@ab2c1 ~]# grep itaig /etc/passwd
[root@ab2c1 ~]# grep itaig /etc/shadow
[root@ab2c1 ~]# userdel -rf itaig
userdel: cannot remove entry 'itaig' from /etc/passwd
[root@ab2c1 ~]#

I have the exact same problem in other servers as well but i can't find a common ground between them:

[root@amad ~]# userdel itaig
userdel: cannot remove entry 'itaig' from /etc/passwd
[root@amad ~]# useradd itaig
useradd: user 'itaig' already exists
[root@amad ~]# 

How come my user is not displayed in /etc/passwd but still exists on the system? I've checked /etc/nsswitch.conf and found no problem there... What can be done in order to fix this issue?

Edit: The output of strace userdel itaig can be found here: http://pastebin.com/FFkcQ3fj

And the output of strace useradd itaig: http://pastebin.com/twRQ7ps0

Second Edit: It seems that if I manually add my user to /etc/shadow and /etc/group I am then able to delete the user using the command userdel itaig , but even then I'm unable to re-create the user as I get an error that the user already exists. Any help would be appreciated!

[root@ab2c1 ~]# userdel itaig
[root@ab2c1 ~]# useradd itaig
useradd: user 'itaig' already exists
[root@ab2c1 ~]# userdel itaig
userdel: cannot remove entry 'itaig' from /etc/passwd
[root@ab2c1 ~]# grep itaig /etc/passwd
[root@ab2c1 ~]# grep itaig /etc/group
[root@ab2c1 ~]# grep itaig /etc/shadow
[root@ab2c1 ~]# id itaig
uid=509(itaig) gid=510(itaig) groups=510(itaig)
[root@ab2c1 ~]# 

Contents of /etc/nsswitch.conf:

passwd:     files   nis
shadow:     files   nis
group:      files   nis
#hosts:     db files nisplus nis dns
hosts:      files nis dns
bootparams: nisplus [NOTFOUND=return] files
ethers:     files
netmasks:   files
networks:   files
protocols:  files
rpc:        files
services:   files
netgroup:   nisplus
publickey:  nisplus
automount:  files nisplus
aliases:    files nisplus

I wonder where the information of the id command comes from:

[root@ab2c1 ~]# grep itaig /etc/passwd
[root@ab2c1 ~]# grep itaig /etc/shadow
[root@ab2c1 ~]# grep itaig /etc/group
[root@ab2c1 ~]# id itaig
uid=509(itaig) gid=510(itaig) groups=510(itaig)
[root@ab2c1 ~]#