{update} I assume that they have to wait for a connection from someone to exchange a piece of the movie though. It is possible to connect to a tracker, falsely advertise the percentage of the file that you have, and just sit there disallowing connections. Unless you transfer something other than communication w/ the tracker I don't know how they could find that you've infringed copyright. [Maybe someone should purposely do this to try and get sued by them.]
Is it illegal to set up a shop that purports to sell illegal devices, even though you don't actually have any illegal devices and never buy or sell an illegal device?
AFAIK, you can't download a torrent without participating in seeding it (at least while you're downloading it). Assuming that whomever is gathering the IP addresses is an authorized representative of the copyright holder, they are actively involved in distributing the video (at least while they're collecting IP addresses).
So, a defendant could claim "At the time you caught me downloading it, an authorized representative of the copyright holder was publishing the content on BitTorrent".
Of course, the problem is that the law isn't logical ;)
They could be publishing data, but you'd have to prove that they weren't just uploading bogus data into the stream. BitTorrent hashes all of the chunks it downloads, but that doesn't prevent someone from constantly uploading bogus data that is only rejected once you've downloaded it. [IIRC, there are clients that will blacklist peers that consistently send corrupt chunks though.] They could just claim that they were uploading random data, and you would have to have some way to refute that (which you wouldn't unless you keep an audit trail of all peers you connect to over BitTorrent).
http://www.austlii.edu.au/cgi-bin/sinodisp/au/cases/cth/FCA/...
starting at about paragraph 110. They are coy about the details, I suppose to make circumvention harder or something.