Thanks for letting us know about this. The behavior you have described is due to a known bug in our system that we expect to have resolved as part of our next major site update which is scheduled to take place around 10/28/08.
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .