As of revision 143, the query_for_record method fails when working in a single_index environment. The problem starts with the parameters -query_for_record only receives the id of record to be queried. It then attempts to construct the class with aaf_configuration[:class_name] but this approach will not work with polymorphic index members. The klass and id should be passed to query_for_record.
For example, if records of class Medium and Person is stored in the single_index, then calling query_for_record will only ever work with the one class that is stored in aaf_configuration[:class_name].