ssh password less login in cygwin lead to no privilege?

I installed a cygwin+openssh on windows 2003 base on instructions from

ssh administrator@xxxxxxxxxxxxx and enter password can login. run
diskpart command works.

i added my to remote authorized_keys file and now can login
without asking for password. then strange thing happen here. running
diskpart told me that i can not connect to management service, which is
a sign of no enough privilege. (my normal user on windows can not run
diskpart because of no enough privilege.)

i remove the entry from authorized_keys file and login with password
again, i still can NOT run diskpart.

i restart sshd in cygwin and then i can run diskpart after login with

so it seems that ssh perform differently here. any idea on this?

my intention is to use ssh to automate some windows management tasks, so
i need to have administrator privilege in ssh.

please cc to me, i am not on this list.

Thanks and wish all of you a wonderful new year!