In file nodesender.c there is statement like this:
/* Find updated records */
result = DBselect("select curr.tablename,curr.recordid,prev.cksum,curr.cksum,prev.sync "
"from node_cksum curr, node_cksum prev "
"where curr.nodeid=%d and prev.nodeid=curr.nodeid and "
"curr.tablename=prev.tablename and curr.recordid=prev.recordid and "
"curr.cksumtype=%d and prev.cksumtype=%d "
"union all "

This statement returns not only updated records but also records which are up to date.
In my opinion this statement should look more like this:
/* Find updated records */
result = DBselect("select curr.tablename,curr.recordid,prev.cksum,curr.cksum,prev.sync "
"from node_cksum curr, node_cksum prev "
"where curr.nodeid=%d and prev.nodeid=curr.nodeid and "
"curr.tablename=prev.tablename and curr.recordid=prev.recordid and "
"curr.cksumtype=%d and prev.cksumtype=%d and curr.cksum<>prev.cksum"
"union all "