Mandatory Profile's field is not mandatory

I have added in profile admin/user/profile one new field:
- checkbox
- Visibility: Private field, content only available to privileged users.
- Checked: The user must enter a value. AND Visible in user registration form.

This field is in fact visible un registration form, but if user did not check it registration form pass without problem. In Drupal 5.7 it was worked differently, id user did not check this field registration process was stopped.

I need this feature in order to introduce TOC field in my registration form.