Organization first openid-connect auth page with login_hint automatically redirect instead of prefilling field #46999

I'm using the organization feature with a "Organization identity - First Login" flow so that only the email field is available in the login page and then redirect to the proper idP based on the domain and it works fine.

I want to optionally possibly pass the e-mail to prefill the field with the login_hint parameter like this:

var authUrl = $"{ssoUrl}/realms/master/protocol/openid-connect/auth" +
$"?client_id={clientId}" +
$"&response_type=code" +
$"&scope=openid%20profile%20email" +
$"&redirect_uri={_redirect}" +
$"&ui_locales={cultureInfo}" +
$"&login_hint={_viewModel.UserName}" +
$"&state={state}" +
$"&nonce={nonce}";

Now when I use this login_hint parameter, it automatically redirect to the idP instead of prefilling the form. Which is not exactly a good flow for my application because it's not obvious the username from my previous interface will be used in the SSO connection.

Based on the documentation, the parameter kc_idp_hint is what should be used to automatically redirect to the idP page, while login_hint should only be used to prefill the field, but it doesn't seem to be the case?