.htaccess protected wp-admin

hi,

i have protected my wp-admin folder using HTTP Auth via .htaccess. My question is this:

When i enter http://www.mydomain.com/wp-admin/, a 401 error just show without asking me to enter the username and password as defined in the .htpasswd

But if i enter http://www.mydomain.com/wp-admin/index.php, then everything works fine. just as it was supposed to work.

how can i make http://www.mydomain.com/wp-admin/ behave the same way as http://www.mydomain.com/wp-admin/index.php?