If Multiple values in field settings is unchecked, when you delete the file (when you click on Delete and submit), the database columns, i.e. the columns in the cck table (content_content type>), aren't updated. This way, in the $node object, the property representing the field is still filled with the deleted files data.
This way, for example, the Has File view filter won't work!
Comments
Comment #1
quicksketchSee #321537: Files checked for deletion aren't deleted on node creation