Sorry about the extra %, that was my mistake in the post. I used it correctly in my testing.
To answer your first question, yes, it displays correctly in the settings page.
None of the methods I’ve tried work, but truly it’s not a valid mechanism for HTTP Auth logout anyway.
Ideally, there would be a better mechanism for logging out. Do you have any suggestions? The default link puts me in a loop of this page upon “Logout” (I’ve removed the server name):
Server Logout Loop