Document Locking - Replication Bug?

I hope someone has an answer on this issue:

I have a database on the server that is replicated to several users. When user 1 has change a document offline and user 2 has also change that document offline and both users replicate the database again, than they don’t receive a replication conflict. User 1 has lost his changes and will not be notify that there where any changes on that document.

All information is welcome…

Kind regards,

Paul Presser