try the following.
- define a new CCK content type with a filefield, which is set to be required
- create a new node of this content type and upload a file
- edit the node, remove the uploaded file and try to delete the node
---> It will say that a file must be uploaded, because the filefield is required.
- upload a new file and hit delete of the node again
---> Node gets deleted, but the newly uploaded file is not deleted.