Problem with biblio_contributors field

Hello.
I have upgraded from beta3 to beta5. My already existing bibliography entries display both an Author and an Authors field in the Tabular View. Both contain correct values, which probably means that data migration has worked as it should. However, in the Edit Node view, only the Authors field is available. Moreover, updates to this field are silently dropped. This happens when creating new entries, and also when updating existing entries. As a result, new entries are displayed as having `No author information' in the tabular node view.

I understand that I may have to hide/remove the (obsolete?) Authors field. However, there isn't any input box or widget available, in order to populate and edit the Author field.

thank you