What's new in 6.38.3 (2017-Feb-07 09:52):

*) bridge - do not add dynamic hardware STP ports if “master-port” is not capable of hardware STP;
*) bridge - fixed rare crash when hardware STP capable interface gets new “master-port” which already is in bridge;
*) bridge - fixed rare situation when port flapping occurs on bridge ports;
*) bridge - fixed STP/RSTP packet receive on all types of bridge ports;
*) bridge - minor improvements in performance when "master-port" is bridge port;
*) capsman - fixed SGI (Short Guard Interval) support;
*) dhcp - do not listen on IPv4/IPv6 client to IPv6 MLD packets;
*) dude - (changes discussed here: http://forum.mikrotik.com/viewtopic.php?f=21&t=116356);
*) firewall - added "fasttrack" dummy rule to "/ip firewall raw" table;
*) firewall - do not show IPv4 “fastpath” as active if “route-cache” is disabled;
*) firewall - fixed import of exported configuration that had updated "limit" setting;
*) graphing - fixed graphing crash when high amount of traffic is processed;
*) hotspot - fixed rare kernel crash on multicore systems;
*) ike1 - fixed responder xauth trailing null;
*) leds - fixed defaults for RBSXT5HacD2nr2;
*) mmips - improved general stability;
*) rb3011 - fixed noise from buzzer after silent boot;
*) switch - fixed crash when trying to configure second master port on the same chipset (RB3011, RB2011, CCR1009-8G-1S+);
*) usb - added missing USB ethernet drivers to arm & tile architecture;
*) winbox - added "add-relay-info" and "relay-info-remote-id" to DHCP relay;
*) winbox - added H flag to "/ip arp" ;
*) winbox - added missing "use-fan2" and "active-fan2" to "/system health";
*) winbox - allow shorten bytes to k,M,G in bridge firewall just like in “/ip firewall”;
*) winbox - do not hide 00:00:00:00:00:00 MAC address in unpublished ARPs;
*) winbox - fixed matching "connection-state=untracked" connections;
*) winbox - fixed typo in “/system resources pci” list;
*) winbox - make "power-cycle-after" show correct value;
*) winbox - updated fan management menu;
*) wireless - added "station-roaming" setting;
*) wireless - update Thailand country frequency settings;