Creating alerts in Sharepoint 2007

I am trying to create alerts in Sharepoint 2007 on a Blog site I created.

All my alerts work properly on my other sites.

The problem I am having is that alerts don't seem to work when a new comment is added to a post. The only alert I receive is when I add a new category. Is this the behavior of the program, or is there something I am missing?

Thanks for your input!