Interdasting. Your temporary fix has rolled the behavior, for me, back to pre-update behavior, and introduced something new.
I can now log in successfully, without generating a captcha, only when the option "remember me" is toggled. When that option is not toggled, the login attempt fails with no error (just reloads the login page). For me, this is the same as the behavior has always been, before the update.
The new behavior is that now, when I attempt to log out, I get:
"You were not logged out, as the request did not match your session. Please contact the board administrator if you continue to experience problems."
The page then shortly reloads to the index page.
Additionally, when I attempt to submit a post after the failed logout, I get a "The submitted form is invalid" error.