sudo -K/-k ineffective

[me]

Hi,

Upon doing sudo <some-command> as a normal user (non-root), sudo asks for
password only once, subsequent invocations of sudo doesn't ask for password
- even though I do sudo -k or sudo -K in between.
Although sudo starts asking for password after the time stamp expiry.

in other words:

% sudo mkdir /newdir
<sudo asks for password authentication, creates the directory after
successful authentication>

% sudo -k

% sudo -K

% sudo mkdir /another_new_dir
<sudo don't ask for password authentication, and creates the directory>

In sudoers file, NOPASSWD is NOT set.
here is my sudeors file: http://pastebin.com/WFnXCLE1

Output of "uname -a":
FreeBSD foo.bar 8.1-RELEASE FreeBSD 8.1-RELEASE #0: Mon Jul 19 02:55:53 UTC
2010
root at almeida.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC i386

Is this known bug? If not, then it might have security implications.

Regards,
Gurpreet Singh
-- 
Life is not fair. Get used to it. .... Be nice to nerds. Chances are you'll
end up working for one.