I cannot confirm that. I just tried myself with examples/experiment/frontend.cxx, removed the RO_ODB, and the trigger events did NOT get copied to the ODB.

Actually you can debug the code yourself. The relevant line is in mfe.cxx:2075:

   /* send event to ODB */
   if (pevent->data_size && (eq_info->read_on & RO_ODB)) {
      if (actual_millitime - eq->last_called > ODB_UPDATE_TIME) {
         eq->last_called = actual_millitime;
         update_odb(pevent, eq->hkey_variables, eq->format);
         eq->odb_out++;
      }
   }

so if read_on is equal 1, the function update_odb should never be called.

So the problem must be on your side.

Best,
Stefan