Hi Peter, you can choose which system could be the leading for you. In our UI templates CRM is the leading system. If you prefer to use IS-U as a leading, it is also possible and some customers choose that. If there is a lock in object in CRM, which is being modified from MCF, there will be an error message. If there is a lock on object in ERP, but MCF updates CRM object, well the Bdoc replication has to take care of it, and eventually it will get replicated.
Yevgen