I believe this is a bug.
1. Set up permalinks like %author%/%year%/%monthnum%/%postname%
2. Write a post as admin
3. Publish post
4. Edit the post author to some other non-admin author
5. Save post
6. View updated post with new url (i.e. author changed)
I continue to get a 404 for the updated post. Note that a related issue might be the previewed permalink in 1 - 6 lacks any author, just the remainder of the permalink