The reference scope is currently defined as follows:
(Select UID_ADSForest from ADSForest where DistinguishedName = '$CP_ADRootdn$')
When a child domain is synced, "CP_ADRootdn" is the DistinguishedName (DN) of the child domain.
But the DN in ADSForest is always the DN of the parent domain. So the reference scope does not result in a site anymore.
The correct reference scope is:
(Select UID_ADSForest from ADSDomain where DistinguishedName = '$CP_ADRootdn$')
This is a product defect (32965).
This will be fixed in a future release of the product. If you require this immediately corrected, please contact Support for a hotfix referencing the defect ID 32965.