inserting

ldap_set_option($connresult, LDAP_OPT_REFERRALS, 0);

around line 1315 like this:

if (!empty($this->config->version))

ldap_set_option($connresult, LDAP_OPT_REFERRALS, 0);

if (!empty($binddn)) {
//bind with search-user

Without this option being set the following errors will occur (you need to have debug messages turned on to see this)

Warning: ldap_search(): Search: Operations error in /moodle/auth/ldap/auth.php on line 1380

Warning: ldap_first_entry(): supplied argument is not a valid ldap result resource in /moodle/auth/ldap/auth.php on line 1388

Not sure what impact this will have on other ldap authenication schemes. It should probably be wrapped with a test for selection of MS Active Directory as source.