Jira Issue CRM-21666 still exists in 5.8.1
https://issues.civicrm.org/jira/browse/CRM-21666
CRM/Mailing/DAO/Mailing.php
and
CRM/Mailing/BAO/Mailing.php
still have a discrepancy regarding the naming of the mailing_date field
messageNotice: Undefined property: CRM_Mailing_BAO_Mailing::$mailing_modified_date in CRM_Mailing_BAO_Mailing::report()