I created a new role that includes 'edit_post' capability; however, anyone assigned to this role does not show-up in the AUTHORS meta-box as someone to whom the Post can be attributed.
My new role actually supports edit_post, edit_published_posts, delet_posts, delete_published_posts, publish_posts, read_posts in addition to a couple of custom capabilities.
This was strange, so i wrote a quick little loop to show me all of the blog members who have 'edit_post' capability. The only ones that it would reported with that capability were Administrators.
Of course, changing a user to have a built-in role (e.g. Editor or Author) and, magically, they're reported as having the capability.
Is there some mystical incantation that I'm supposed to embark before capabilities are "active"?