Steps to reproduce the issue

Staging (3.8.4-dev), I've a regression on front-end login I suspect #19099 , as I'm getting a 404 with modern routing.
I've a standard login form with "The Menu Item Login Redirect" toward a menu item. The referring page
"http://localhost/staging/index.php/fr/?option=com_users&view=login" is generating the following in the Redirects components "http://localhost/staging/index.php/fr/component/users/?task=user.login"

Expected result

Login as usual

Actual result

404 and "index.php/fr/component/users/?task=user.login" is logged in the Redirects components

System information (as much as possible)

both Apache + PHP 5.4.23 and XAMPP with PHP 5.6.24

Additional comments

Woking fine on 3.8.3