[sudo-users] Why sudo(1) asks for password when stdout and stderr are redirected?

[Vladimir Barbarosh]

Hi.

robot:
        #!/bin/bash
        sudo echo apple
        sudo cat << EOF
        banana
        EOF

command prompt:
        $ sudo true
        [sudo] password for vb:
        $ ./robot
        apple
        banana
        $ ./robot > /dev/null
        $ ./robot &> /dev/null
        [sudo] password for vb:

Why sudo(1) asks for password when stdout and stderr are redirected?

I already asked this question on http://superuser.com (http://bit.ly/hSvAXk).

>From this answer (http://bit.ly/fqpapQ) I conclude that this is a bug because
"on my system (ubuntu 10.04), sudo asked for my password when I
redirected stdout." But on my system (Debian 6.0.1) everything ok when I
redirect only stdout.

I read Wikipedia page (http://en.wikipedia.org/wiki/Sudo), and FAQ
(http://www.sudo.ws/sudo/troubleshooting.html). I skim manual page
(http://www.sudo.ws/sudo/man/1.8.1/sudo.man.html) and even do
some googling, but still I can't answer why sudo(1) ...

Can anyone help me please?

-- 
Vladimir Barbarosh