Audit trail in oracle 9i

Hi all,

   I have been used 9i on aix.

   I just takeover this db. My db already actived audit trail but I recognize some stranges:

   I checked some parameters:

   audit_trail = DB

   audit_file_dest=/xbank/oracle/REPORTs/audit/

   audit_sys_operations =FALSE

   When select data from SYS.AUD$ I can view records from it. But when I log on by user with SYSDBA, oracle recorded data and generated file to /xbank/oracle/REPORTs/audit/ ==> why ? I configured audit_trail = DB not OS and audit_sys_operations =FALSE not TRUE ? Infomations detail from audit file look like:

Audit file /xbank/oracle/REPORTs/audit/ora_76068.aud