Multiple LDAP backends not working

When configuring multiple LDAP backends, logins are not possible. Only when using a single LDAP server it is working as expected.

Tried the following configuration that doesn't work:

$config['auth_ldap_server']  = array("ldap1.server.ext","ldap2.server.ext");

Also it does not work when the config rule is disabled/removed and backends added in the config in the web interface through Global Settings -> Edit -> Authentication -> LDAP servers. 

Configuration that does work:

$config['auth_ldap_server']  = "ldap1.server.ext";

Maybe there isn't support for multiple backends, but the field in the web interface indicates that multiple backends can be provided.

Version: r9172