NAT Loopback problem on RT-AC3200

[scottegos2]

I'm using RMerlin 378.51 final build on my RT-AC3200. I have an asuscomm.com ddns domain name set up. I use IPP on my Lexmark printer, so I have WAN port 631 forwarded to my printer's port 631 (forwarding both tcp and udp, though probably tcp only would suffice). So on my Win 8.1 laptop, I have a printer defined on ipp port http://xxx.asuscomm.com:631. This works fine with the Asus NAT Loopback setting, but neither my browser nor the print spooler subsystem sees the printer when I use the (default) Merlin setting.