I'd argue it's odd that they (or LDAP) normalise input in the first place. I can sort-of understand username normalization to avoid having both "admin" and "Admin" accounts, but that check only needs to be done when creating an account, when logging in it should not accept "Admin" as valid for account "admin".

But I'm neither a security person nor have I done much with authentication since my 2000's PHP hobbying. I suspect an LDAP server has to deal with or try and manage a lot of garbage input because of the sheer number of integrations they often have.