Changing the admin folder name problem

[lat9]

I have changed the name of my admin foldder and now I'm having a problem when signing in.

When I go to:

https://www.mywebsite.com/myadminpage/index

I'm correctly sent to the login page. I enter my username and password and click Enter,
but then I'm incorrectly sent to the 'Page Not Found' page, and the URL is missing the 'index', like this:

https://www.mywebsite.com/myadminpage

If I now manually add 'index' to the URL then I'm sent correctly to my admin home page.

Why is 'index' automatically removed from the URL when I'm trying to login?

Are you using Ceon URI Mappings? If so, the site's .htaccess includes the admin-directory's name as one of the URLs to "leave alone" and that file needs to be updated, too.