This can hardly be called a bug, but when I signed up to post on these forums, I didn't know whether or not I had an account, so I tried signing in. Turns out I don't, but when you try to log in with an account that doesn't exist, you get the message "The username or email afawef does not exist here on WordPress.org. Register it?"
That "Register it?" link only takes you back to another login form, not the appropriate registration form. I'm not sure the best place to post this, but I thought I would let someone know.