Here is an example of a document that was being used as a holding place for job postings. The postings were posted as attached Word documents. Periodically, old attachments would be removed and new ones added. However, this was not triggering email notifications.

Does this behaviour differ depending on whether the document has been created as a Write New Document or an Upload File?

As it stands it's confusing. The user was reasonably assuming that notifications would be sent, since she had not checked the "Minor update/do not send notifications" box.

My personal preference would be for notifications always to be sent in the event that either body or attachments have changed, and the checkbox is not ticked.