It may be an issue with the server version rather than the Notes client.
There have been issues with unread marks counts when replicating on Domino 8.5 servers
Adding the following notes.ini setting on the server: REPL_SYNC_ALL_UNREAD=1, while having the server on at least Domino 8.5.3 FP1 should resolve most unread marks issues,
More information here:
http://www-01.ibm.com/support/docview.wss?uid=swg27023614