ConfigMgr SCCM 2012 SP1 Mac client registration fails KB Hotfix 2806021. Microsoft has released one more KB article 2806021 to fix the ConfigMgr 2012 SP1 client registration issue/s with Mac OS workstations.
It seems this is applicable for https communications with PKI certificates.
ConfigMgr SCCM 2012 SP1 Mac client registration fails KB Hotfix 2806021
When you try to register a Mac client in System Center 2012 Configuration Manager Service Pack 1 (SP1), the registration process fails. When you check the MP_RegistrationManager log in this situation, you see the following error: The certificate chain processed correctly but terminated in a root certificate not trusted per ConfigMgr CTL.
More details about this issue here.