Mailbox being skipped from synchronization when added to collection by group (4305935)

If mailbox was added to synchronization collection by group it may be skipped from synchronization under certain circumstances. However the same scenario works if the mailbox was directly added to the synchronization collection. The following  shows in Mail Source Agent log:

CADQueue::ExpandContainers TraceMsg 4504 Container   '/o=Org.Name/ou=Administrative Group Name/cn=Recipients/cn=dl.name' contains x items.
CADQueue::AddChildItem Warning 4512 Skipping item ''/o=Org.Name/ou=Administrative Group Name/cn=Recipients/cn=user.name' because the item already exist in the collection 'collection.name'.