And though it took me to the usual page which has "Go back to the page you were previously viewing", it STILL HAD a Logout option on that page.
I "Logged Out" again and the option disappeared.
FWIW I was using Google Chrome when it happened. I have noticed it before on GC, but for FFox I haven't yet noticed it.
Edit, a few minutes later.
Though it still had the logout option and still said "Good afternoon ameerat42", it had logged out properly, because when I clicked on "return to previous" I had to log back in.