If updating a post's author and assigning a WP user (not a CAP guest author), the post_author field isn't updated even though the author taxonomy term is updated. Because the term is updated properly, the post will render with the correct author byline, but the post will not appear in any WP queries targeting the post_author ID or name. Verified in v3.5.6.

To replicate:

1. Publish a post assigned to the site's default author.
2. Using the CAP sidebar UI, add another WP user (not guest author) and remove the original author. Update the post.
3. View the post and observe that the new WP user is shown as the byline.
4. However, using WP CLI, get the post ($ wp post get <ID>) and observe that the post_author field still shows the default author's ID, not the second WP user's.