Okay, I'm experimenting with this on localhost before activating it on my site. I wanted to test to see if hiding the back end broke any other plug ins before I did it.
So I turned it on. Then I tried the 'old' links from a different web browser. As far as I can tell, it's accessing the log in the usual way. It's not adding the secret key or anything.
Is there any reason it would not work on localhost? Am I missing a step?