Still able to block/unblock Administrator account even if permission not granted

Problem/Motivation

When I try to block Administrator account by selecting it in the checklist of users and by applying block all selected accounts, it gives a warning that the administrator account cannot be blocked, but it actually did block the administrator account.

Drupal 7.15 used, fresh install with Role Assign module also installed.

Proposed resolution

1. When user is not given the right to administer a user don't allow it to be checked in the list.
2. Allow th right to hide a user from the list (Administrator)
3. Allow the module to work without the 'administer users' permission