Whats the deal with FTP port forwarding and AE?

So, I do lighting home automation. The product I use I can have access to remotely so that I can easily update the configs for my clients without having to go to their house. This requires me to access ports 23 and 21...I know those are very common ports and don't like to be open to the internet, but that isn't my choice and I can't change ports.

So, I have done a number of homes with no issues. My latest one had an Airport Extreme. No problem I thought. Dumb me. I could initially connect via port 23 no problem. However, as soon as I tried to upload files the FTP failed to connect. I have an AE too and started playing with FTP access. I had NO success UNLESS I enabled default host under NAT and had it forward to the appropriate IP address. Then it worked.

So, I had the home owner change that setting on his AE. Eureka...it worked.

My question is...is FTP port forwarding still broken in AE and 7.4.2? What gives?