Public Folders and Attachments

Situation: We have Exchange 5.5 and are using the Public folders to share some excel files. Within each folder are separate postings with one excel attachment each. Users will then open up the appropriate posting, edit the file as needed, save and close. All users have edit permissions but no delete permission.

The problem: Although the user has no delete permission, they are still able to remove the excel attachment from the post. The posting will still be there but the attachment is gone.

Has anyone seen this and been able to stop it from happening? Thanks