joining AD user to existing metaverse peson object is impossible ?

There is one person ojbect in metaverse which is imported from AD MA(say AD1).

Same user's mailbox exists in other Forest and I tried to import by AD MA(say AD2),

but join-resolution error happened.

If in attribute flow , join rule from datasource(user)  to person object is defined,

is it impossible to join data source( user) object to existing metaverse object ? 

AD2_MA with  DN CS AD2_MA user someuser  attempts to join when it should be projected.  There is another authoritative object representing the same entity in the metaverse: CS AD1_MA user someuser. This object will not be propagated to any other forests until this conflict is resolved by removing or modifying one of the objects so that they no longer collide.