After upgrading the firmware on a Draytek Vigor 2830 port forwarding on port 443 stopped working, after a bit of digging around in the router setting i noticed a new ‘SSL VPN’ section had been added, under General Settings i changed the port to 8443 as we don’t use this feature, port 443 is now forwarding correctly again.
See http://www.draytek.co.uk/support/kb/kb_sslvpn_troubleshooting.html for more info