The `PhabricatorRepositoryCommit::updateAuditStatus` method (see https://secure.phabricator.com/diffusion/P/browse/master/src/applications/repository/storage/PhabricatorRepositoryCommit.php;7705f452d238f85d7e3f39391ea0701696679236$209) doesn't consider manually added auditors (via "add auditors" action on commit detail page) as criteria for changing commit audit status to "needs audit".
I think, that not only `PhabricatorAuditStatusConstants::AUDIT_REQUIRED` but also `PhabricatorAuditStatusConstants::AUDIT_REQUESTED` constant should trigger `$any_need` variable.