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.