I was trying to use Transmission's Web Interface, and it worked perfectly. I could access it via http://localhost:8080/transmission/web/, I could use my local IP, I could use 127.0.0.1, I could, after port-forwarding, even use my actual IP. A DNS connection even succeeded!

I was annoyed by the :8080 tacked onto the URL, and wanted to remove it, so, I went into Transmission's settings and changed it to port 80. All of a sudden, I couldn't connect via any method! They all failed. Even pressing the "Open web client" button in Transmission's settings didn't work. (just a generic "could not establish connection" message, incase you were curious.)

NOTE: I do not have Apache or any other server software installed.

I then, in a panic, switched back to port 8080, and everything was fine. Another try on 80, and failure. Restarting Transmission didn't fix anything, either. (On a hunch, I tried connecting to the :8080 url while I'd set it to port 80, just to see if it was still using the old port. It wasn't.)

Anyway, this isn't a critical issue, but I'd really like to be able to use port 80 for my web client! (well, I'd actually like to be able to use 443, but that's another question...)