When choosing a custom FTP server to get the package files from, snarf does not connect to the server if it's address does not start with ftp.*. It gives back a "connection refused" message in the logging terminal. Problem is that snarf is called like "snarf $FTP_SERVER$FTP_DIR/blah", without a leading ftp:// denoting the protocol. Usually not a problem, since snarf "guesses" the protocol correctly when using an ftp.blah.com server, but it failed horribly on "fulvus.foxden.local".
I did not try using an IP, but a similar error is expected.
Unfortunately, when entering "ftp://fulvus.foxden.local" as a custom server, the snarfing of packages.txt works fine, but pacman throws a segfault later when trying to install the packages. This is a bug I'll report seperately, and is caused by the generated line "ftp://ftp://fulvus.foxden.local/arch/current" in the /etc/pacman.conf.