Jamil on "[Plugin: Co-Authors Plus] All Authors Suddenly Vanished from posts"

I have the same issue and have posted more details in this thread, since it highlights another problem with the update.

http://wordpress.org/support/topic/duplicates-on-authors-page

When I disabled the plugin the authors showed up but they already did in the front end anyway. The also show up in the backend with coauthors plus disabled but once enabled, they disappear from the back end, and only one author appears (as before).