This plugin has worked fine for me up until today. Some background: Sometimes it takes a while for a co-author to subscribe and get upgraded to an author. In the meantime, I will get his/her post up in draft form and ready to be published. Then when the author finally subscribes, I upgrade him/her and publish the post. So today, after adding a new co-author to a post, the link that is the co-author's name takes you to the author description for the first author. Also, the new co-author's name occasionally disappears from the post.
When I upgraded to WP 3.01 a few months ago, I found that Role Manager didn't work. So I changed to Capability Manager. I don't know if the issue is WP 3.01, Capability Manager or Co-Authors Plus. I have deactivated Capability Manager and that had no effect.