The edited document again i edit and not updated on couchbas

Question

I am following the below steps.

1.Pull push replication get all documents from couchbase server to couchbase lite on my machine.
2.And suppoes document id 'x' i update document on couchbase lite and then start pull push replication
3.The x document updated successfully on couchbase server
4.again i am start step 1
5.Updated document get correct from couchbase server to couchbase lite
6.Again i update the document id 'x' and then start pull push replication field not reflected on couchbase server

Note : First time on each document edited successfully
the edited document again i edit and not updated on couchbase server

please tell me what i am missing