Thanks for the update! This one had me really confused. One down, one to go.
OK, found it. Looked in the logs after rebooting and found out that the redirect on error (Link or Wan) was turned on. After the connection came up, it seems that the redirect stayed on. I disabled it and the pages now load correctly.
Log just for kicks:
Oct 15 18:07:50 WAN Connection: Ethernet link down.
Oct 15 18:07:50 stop_nat_rules: apply the redirect_rules!
Oct 15 18:07:50 dnsmasq[629]: exiting on receipt of SIGTERM
Oct 15 18:07:50 dnsmasq[4184]: started, version 2.72test3 cachesize 1500
Oct 15 18:07:50 dnsmasq[4184]: warning: interface ppp1* does not currently exist
Oct 15 18:07:50 dnsmasq[4184]: asynchronous logging enabled, queue limit is 5 messages
Oct 15 18:07:50 dnsmasq-dhcp[4184]: DHCP, IP range 192.168.5.2 -- 192.168.5.254, lease time 1d
Oct 15 18:07:50 dnsmasq[4184]: read /etc/hosts - 5 addresses
Oct 15 18:07:50 dnsmasq[4184]: using nameserver 209.18.47.61#53
Oct 15 18:07:50 dnsmasq[4184]: using nameserver 209.18.47.62#53
Oct 15 18:07:55 WAN Connection: Ethernet link up.
Oct 15 18:07:55 rc_service: wanduck 510:notify_rc restart_wan_if 0
Oct 15 18:07:55 dnsmasq[4184]: read /etc/hosts - 5 addresses
Oct 15 18:07:55 dnsmasq[4184]: using nameserver 209.18.47.61#53
Oct 15 18:07:55 dnsmasq[4184]: using nameserver 209.18.47.62#53
Oct 15 18:07:55 stop_wan(): perform DHCP release
Oct 15 18:07:56 kernel: Attempt to kill tasklet from interrupt
Oct 15 18:07:56 kernel: br0: port 1(vlan1) entering forwarding state
Oct 15 18:07:56 kernel: device eth0 left promiscuous mode
Oct 15 18:07:56 kernel: device eth0 entered promiscuous mode
Oct 15 18:07:56 kernel: br0: port 1(vlan1) entering forwarding state
Oct 15 18:07:56 kernel: br0: port 1(vlan1) entering forwarding state
Oct 15 18:07:56 miniupnpd[715]: ioctl(s, SIOCGIFADDR, ...): Cannot assign requested address
Oct 15 18:07:56 miniupnpd[715]: Failed to get IP for interface eth0
Oct 15 18:07:56 miniupnpd[715]: SendNATPMPPublicAddressChangeNotification: cannot get public IP address, stopping
Oct 15 18:07:56 dnsmasq[4184]: read /etc/hosts - 5 addresses
Oct 15 18:07:56 dnsmasq[4184]: using nameserver 209.18.47.61#53
Oct 15 18:07:56 dnsmasq[4184]: using nameserver 209.18.47.62#53
Oct 15 18:07:56 dnsmasq[4184]: read /etc/hosts - 5 addresses
Oct 15 18:08:00 WAN Connection: ISP's DHCP did not function properly.
Oct 15 18:08:06 WAN Connection: Ethernet link up.
Oct 15 18:08:06 rc_service: wanduck 510:notify_rc restart_wan_if 0
Oct 15 18:08:07 dnsmasq[4184]: read /etc/hosts - 5 addresses
Oct 15 18:08:07 stop_wan(): perform DHCP release
Oct 15 18:08:07 kernel: Attempt to kill tasklet from interrupt
Oct 15 18:08:07 kernel: br0: port 1(vlan1) entering forwarding state
Oct 15 18:08:07 kernel: device eth0 left promiscuous mode
Oct 15 18:08:07 kernel: device eth0 entered promiscuous mode
Oct 15 18:08:07 kernel: br0: port 1(vlan1) entering forwarding state
Oct 15 18:08:07 kernel: br0: port 1(vlan1) entering forwarding state
Oct 15 18:08:09 dnsmasq[4184]: read /etc/hosts - 5 addresses
Oct 15 18:08:12 dnsmasq[4184]: read /etc/hosts - 5 addresses
Oct 15 18:08:12 dnsmasq[4184]: using nameserver 192.168.100.1#53
Oct 15 18:08:12 rc_service: udhcpc 4205:notify_rc start_firewall
Oct 15 18:08:12 kernel: HTB: quantum of class 10002 is big. Consider r2q change.
Oct 15 18:08:12 kernel: HTB: quantum of class 10060 is big. Consider r2q change.
Oct 15 18:08:12 start_nat_rules: apply the nat_rules(/tmp/nat_rules_eth0_eth0)!
Oct 15 18:08:12 rc_service: udhcpc 4205:notify_rc stop_upnp
Oct 15 18:08:12 rc_service: waitting "start_firewall" via udhcpc ...
Oct 15 18:08:12 dnsmasq[4184]: exiting on receipt of SIGTERM
Oct 15 18:08:12 dnsmasq[4245]: started, version 2.72test3 cachesize 1500
Oct 15 18:08:12 dnsmasq[4245]: warning: interface ppp1* does not currently exist
Oct 15 18:08:12 dnsmasq[4245]: asynchronous logging enabled, queue limit is 5 messages
Oct 15 18:08:12 dnsmasq-dhcp[4245]: DHCP, IP range 192.168.5.2 -- 192.168.5.254, lease time 1d
Oct 15 18:08:12 dnsmasq[4245]: read /etc/hosts - 5 addresses
Oct 15 18:08:12 dnsmasq[4245]: using nameserver 192.168.100.1#53
Oct 15 18:08:13 rc_service: udhcpc 4205:notify_rc start_upnp
Oct 15 18:08:13 rc_service: waitting "stop_upnp" via udhcpc ...
Oct 15 18:08:13 miniupnpd[715]: shutting down MiniUPnPd
Oct 15 18:08:14 WAN Connection: WAN was restored.
Oct 15 18:08:14 ddns: clear ddns cache file for server/hostname change
Oct 15 18:08:15 miniupnpd[4276]: HTTP listening on port 41302
Oct 15 18:08:15 miniupnpd[4276]: Listening for NAT-PMP/PCP traffic on port 5351
Oct 15 18:08:15 ddns update: ez-ipupdate: starting...
Oct 15 18:08:30 ddns update: error connecting to ns1.asuscomm.com:80
Oct 15 18:08:30 ddns update: asusddns_update: 1
Oct 15 18:08:30 dhcp client: bound 192.168.100.10 via 192.168.100.1 during 20 seconds.
Oct 15 18:08:46 dnsmasq[4245]: read /etc/hosts - 5 addresses
Oct 15 18:08:46 dnsmasq[4245]: using nameserver 192.168.100.1#53
Oct 15 18:08:46 miniupnpd[4276]: ioctl(s, SIOCGIFADDR, ...): Cannot assign requested address
Oct 15 18:08:46 miniupnpd[4276]: Failed to get IP for interface eth0
Oct 15 18:08:46 miniupnpd[4276]: SendNATPMPPublicAddressChangeNotification: cannot get public IP address, stopping
Oct 15 18:08:49 WAN Connection: ISP's DHCP did not function properly.
Oct 15 18:08:49 stop_nat_rules: apply the redirect_rules!
Oct 15 18:08:49 rc_service: udhcpc 4286:notify_rc start_firewall
Oct 15 18:08:49 dnsmasq[4245]: read /etc/hosts - 5 addresses
Oct 15 18:08:49 dnsmasq[4245]: using nameserver 209.18.47.61#53
Oct 15 18:08:49 dnsmasq[4245]: using nameserver 209.18.47.62#53
Oct 15 18:08:49 start_nat_rules: apply the nat_rules(/tmp/nat_rules_eth0_eth0)!
Oct 15 18:08:50 dnsmasq[4245]: exiting on receipt of SIGTERM
Oct 15 18:08:50 kernel: HTB: quantum of class 10002 is big. Consider r2q change.
Oct 15 18:08:50 kernel: HTB: quantum of class 10060 is big. Consider r2q change.
Oct 15 18:08:50 dnsmasq[4327]: started, version 2.72test3 cachesize 1500
Oct 15 18:08:50 dnsmasq[4327]: warning: interface ppp1* does not currently exist
Oct 15 18:08:50 dnsmasq[4327]: asynchronous logging enabled, queue limit is 5 messages
Oct 15 18:08:50 dnsmasq-dhcp[4327]: DHCP, IP range 192.168.5.2 -- 192.168.5.254, lease time 1d
Oct 15 18:08:50 dnsmasq[4327]: read /etc/hosts - 5 addresses
Oct 15 18:08:50 dnsmasq[4327]: using nameserver 209.18.47.61#53
Oct 15 18:08:50 dnsmasq[4327]: using nameserver 209.18.47.62#53
Oct 15 18:08:50 rc_service: udhcpc 4286:notify_rc stop_upnp
Oct 15 18:08:50 rc_service: waitting "start_firewall" via udhcpc ...
Oct 15 18:08:51 rc_service: udhcpc 4286:notify_rc start_upnp
Oct 15 18:08:51 rc_service: waitting "stop_upnp" via udhcpc ...
Oct 15 18:08:51 miniupnpd[4276]: shutting down MiniUPnPd
Oct 15 18:08:51 watchdog: start ddns.
Oct 15 18:08:51 rc_service: watchdog 528:notify_rc start_ddns
Oct 15 18:08:52 ddns update: ez-ipupdate: starting...
Oct 15 18:08:52 ddns update: connected to ns1.asuscomm.com (103.10.4.108) on port 80.
Oct 15 18:08:53 ddns update: Asus update entry:: return: HTTP/1.1 200 OK^M Date: Wed, 15 Oct 2014 22:08:52 GMT^M Server: Apache/2.4.9 (Unix) PHP/5.5.14 OpenSSL/1.0.1h^M X-Powered-By: PHP/5.5.14^M Content-Length: 0^M Connection: close^M Content-Type: text/html^M ^M
Oct 15 18:08:53 ddns update: retval= 0, ddns_return_code (,200)
Oct 15 18:08:53 ddns update: asusddns_update: 0
Oct 15 18:08:53 ddns: ddns update ok
Oct 15 18:08:53 ddns: IP address, server and hostname have not changed since the last update.
Oct 15 18:08:53 dhcp client: bound ************ (I removed this) during 86400 seconds.
Oct 15 18:08:53 miniupnpd[4364]: HTTP listening on port 45980
Oct 15 18:08:53 miniupnpd[4364]: Listening for NAT-PMP/PCP traffic on port 5351
Oct 15 18:08:55 WAN Connection: WAN was restored.