This may be a security issue but after tinkering for hours with the below ldap auth function (edi01 at gmx dot at), I discovered that the ldap_bind function will return true if you enter a valid username AND a NULL value!
so if that function were to receive something like $username = 'someuser' and $password = '', it would return true. As long as it isn't a null value the function will work as expected. Might as well check if it is null or empty then.