[Plugin: Co-Authors] coauthors_wp_list_authors doesn’t link to author page

I have a blog where only one author actually publishes posts, but several other authors are assigned as co-authors in his posts. However, when trying to display a list of authors with links to each author’s page using the following function:

coauthors_wp_list_authors('show_fullname=1&optioncount=0&hide_empty=0&exclude_admin=0');

The co-authors all show up in the list, but with no links to their author page. While the posts they were assigned to do show up on their author page when I access it directly, I have to create the list manually.

http://wordpress.org/extend/plugins/co-authors/