added a comment - - edited
Oliver Behnke In the meantime, could you quickly run a DB query in the BOINC database, and find all users with 'blank' usernames. Something like
SELECT u.id,u.name,u.email_addr,du.uid,du.name,du.mail FROM EinsteinAtHome.user as u INNER JOIN drupal.boincuser as bu ON u.id=bu.boinc_id INNER JOIN drupal.users as du ON bu.uid=du.uid WHERE u.name='';
I should try and see if I can contact these people and have them change their usernames due to this bug.
Update: I changed the SQL statement to one more sophisticated.