It will have never worked with login/login as far as I know.
login/login is the URL which processes the login information.
You're going to make me check version 1.0 aren't you?
Yep. Since version 1.0 there has always been a check that would generate the available via POST only message:
What may be causing the confusion is that because the login forum has the potential to forward you to a register page, you may sometimes see the URL as login/login, but the fact remains that URL has never been accessible via a direct link. Only by submitting data via the login form.
Submitting data using the login form POSTs that data to the login/login URL.
If on the login form you have opted to register, you are rerouted to the registration page via the login/login URL. But that URL is only valid if it has had data passed to it from the login form, hence why it gives the error.