diff -urN zabbix-2.0.13.org/frontends/php/api/classes/CHostGroup.php zabbix-2.0.13.ZBX-8852/frontends/php/api/classes/CHostGroup.php
--- zabbix-2.0.13.org/frontends/php/api/classes/CHostGroup.php	2014-09-10 18:23:30.000000000 +0900
+++ zabbix-2.0.13.ZBX-8852/frontends/php/api/classes/CHostGroup.php	2014-10-02 18:08:00.000000000 +0900
@@ -444,7 +444,7 @@
 
 					// maintenanceids
 					if (isset($group['maintenanceid'])) {
-						if (!isset($result[$group['groupid']]['maintenanceid'])) {
+						if (!isset($result[$group['groupid']]['maintenances'])) {
 							$result[$group['groupid']]['maintenances'] = array();
 						}
 						$result[$group['groupid']]['maintenances'][] = array('maintenanceid' => $group['maintenanceid']);