diff -Ndur linux-2.6.32-orig/net/ipv4/tcp_input.c linux-2.6.32-undorttzero/net/ipv4/tcp_input.c
--- linux-2.6.32-orig/net/ipv4/tcp_input.c	2013-06-05 15:47:10.551009408 -0400
+++ linux-2.6.32-undorttzero/net/ipv4/tcp_input.c	2013-06-05 15:49:32.458996663 -0400
@@ -5783,9 +5783,11 @@
 
 				/* tcp_ack considers this ACK as duplicate
 				 * and does not calculate rtt.
-				 * Force it here.
+				 * Fix it at least with timestamps.
 				 */
-				tcp_ack_update_rtt(sk, 0, 0);
+				if (tp->rx_opt.saw_tstamp && 
+					tp->rx_opt.rcv_tsecr && !tp->srtt)
+						tcp_ack_saw_tstamp(sk, 0);
 
 				if (tp->rx_opt.tstamp_ok)
 					tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;