This is not relevant if PHPBB3-16193 ever gets finished, but right now whenever a draft is saved, any attachments which were uploaded for the draft end up permanently orphaned instead of being cleaned from the server. A simple call to delete the orphaned attachments when a draft is saved would stop polluting the server with orphan attachments which are guaranteed not to be used again. See attached patch.
1. Create post
2. Add attachment
3. Save as draft
Expected: Attachments are deleted from the server
Actual: Unrecoverable attachments are left on the server