Why is Oracle producing .aud files for internal sys-statements?

I have recently been in contact with Oracle support regarding an issue where my Oracle 18c database instance is sending audit information for internal statements, much similar to this:

Sun Jan 26 10:25:41 2020 +01:00 LENGTH : '401' ACTION :[147] 'select /*+ opt_param('parallel_execution_enabled', 'false') EXEC_FROM_DBMS_XPLAN */ * from gv$sql_plan where 1=0' DATABASE USER:[1] '/' PRIVILEGE :[4] 'NONE' CLIENT USER:[0] '' CLIENT TERMINAL:[7] 'UNKNOWN' STATUS:[1] '0' DBID:[10] '1325844924' SESSIONID:[1] '0' USERHOST:[26] 'myhost.mydomain.com' CLIENT ADDRESS:[0] '' ACTION NUMBER:[1] '3' Sun Jan 26 10:25:41 2020 +01:00 LENGTH : '375' ACTION :[121] 'SELECT * FROM gv$sql_plan where sql_id = 'a0f1h9d5muwa6' and inst_id = 1 and child_address = hextoraw('00000004FFF16130')' DATABASE USER:[1] '/' PRIVILEGE :[4] 'NONE' CLIENT USER:[0] '' CLIENT TERMINAL:[7] 'UNKNOWN' STATUS:[1] '0' DBID:[10] '1325844924' SESSIONID:[1] '0' USERHOST:[26] 'myhost.mydomain.com' CLIENT ADDRESS:[0] '' ACTION NUMBER:[1] '3'

If you have migrated to Unified Auditing, Oracle states that "audit records are only expected to be generated in database tables and OS spillover files (*.bin) under audit destination path."

However, dynamic SQL statements parsed or executed using DBMS_SQL package are being audited in the conventional *.aud type OS files.

To get rid of these messages piling up in your audit_dump_dir:

alter system set audit_sys_operations=FALSE scope=spfile;
shutdown immediate
startup

If setting audit_sys_operations to FALSE is not desirable, Oracle states that you can request a patch through the following bug number:


Bug 21133343 *.aud file is generated though unified auditing=true and audit_trail=none


Note that you will see the same phenomenon under the mixed-mode or classic auditing.
Oracle does not explisitly say they will provide a patch in this case though.

Documentation from Oracle support: Doc ID 2020881.1: "OS Audit Files *.aud are Still Generated After Migrating to Unified Audit"