Not quite sure... should be the same thing...
but, hey, i've seen stranger things with this firmware....
I personaly never used / setup a Secured FTP server... just standard FTP
But I just did some testing... enabling FTP and puting the checkmark in SSL/TLS
And I tried connecting with CuteFTP localy and it worked fine when using my 192.168.xxx.xxx address
So I tried again from inside my network, but using my external IP, and it worked fine again....
At some point it even substitued my PASV address from my internal 192.168.xxx.xxx to my external IP
So on to the next point... tried accessing my FTP from an external site using my DNS name (DynDNS.org)
and it also worked fine.
The only difference I saw is that my FTP Client never used the MLSD command
just the LIST command.
Im using CuteFTP 8.0 Pro.... not sure how to make it used MLSD instead of LIST....