can’t set comments to “admin needs to approve first” option

Hi!

I have always open without need to approve first the comments in my blog.

But recently I’m having too many problems with some commenters and I need to set comments to be approved first by a moderator (using that option in options/discussion).

But even activating that option, all people can comment in my blog without the required approve… ??

I’m using WP 2.1.3 in a shared hosting using PHP 5.2.1

Any ideas please???

Thanks in advance.