Aggregate num-Items per server is less than total num_items displayed on the UI

Setup a 2 node : 2 Node cluster ( xdcr)
Setup replication between the clusters
Load 1M items on source node

UI display stats [ for bucket for all servers together]
total items = 999k
active items =999k
replica items=999k

UI display stats Per Individual server
active items = 498k
active_items =500k

Sum of the above =998k and not 999k

ketaki@ubuntu-1004-x64-307:~$ /opt/couchbase/bin/cbstats Sourcet:11210 -b bucket-0 all | grep "curr_items"
curr_items: 498514
curr_items_tot: 999169
vb_active_curr_items: 498514
vb_pending_curr_items: 0
vb_replica_curr_items: 500655

ketaki@ubuntu-1004-x64-307:~$ /opt/couchbase/bin/cbstats Destination:11210 all | grep "curr_items"
curr_items: 498514
curr_items_tot: 999169
vb_active_curr_items: 498514
vb_pending_curr_items: 0
vb_replica_curr_items: 500655

Attaching screenshots.