When deciding whether to execute a block of code that deletes users, sync_users() uses incorrect comparison operator (trying to strictly compare a string with a numeral constant). This leads to redundant actions and performance deterioration.

How to fix:
in file auth/ldap/auth.php
replace
if ($this->config->removeuser !== AUTH_REMOVEUSER_KEEP) {
with
if ($this->config->removeuser != AUTH_REMOVEUSER_KEEP) {