In a one-to-many assoiation, ownership lies with the 'many' entity, in your case Attachment. That means that all info about the associated objects will be stored with the Attachment-objects, including changes. When you change an Attachment, the associated Project object will not automatically know that something has changed. You will have to implement this manually, aka make or add to the "Save changes to Attachment"-flow an action that will make a log entry for the associated Project.