Autocompletion from .netrc in Emacs

Question

I use Emacs at work and at home, both on Windows XP, both EmacsW32. On my work computer, if I setup FTP login details for a site, for example:

machine ftp.stackoverflow.com login codinghorror password orange

then if I want to ftp there from Emacs, I just type

/ftp.s<tab>

and it knows from my .netrc that it can autocomplete to

/ftp.stackoverflow.com:

which is exactly what I want. On my home computer, the autocomplete just doesn't work, although it does once I'm on the server, so if I type:

/ftp.stackoverflow.com:public_h<tab>

it will autocomplete the html. Does anyone have any ideas as to why this might be?