Most likely related to ZBX-23210.

There sometimes is an PHP runtime error when unlinking a template. Not sure what exactly causes it, but I could reproduce it with the following scenario:

1. Open Template configuration list
2. Delete the first template (when sorting by name ASC) "AIX by Zabbix agent" (this is simply so that it is easier to follow the scenario)
3. Open the now 1st template "Alcatel Timetra TiMOS by SNMP"
4. Link it with the 2nd template - "Apache ActiveMQ by JMX" and Update
5. Open the 2nd template and link it with 3rd template - "Apache by HTTP", press Update
6. Click the 2nd template again, press "Unlink" to unlink "Apache by HTTP", press Update

Result
PHP runtime error:

Undefined index: flags [zabbix.php:22 -> require_once() -> ZBase->run() -> ZBase->processRequest() -> CController->run() -> CControllerTemplateUpdate->doAction() -> CApiWrapper->__call() -> CFrontendApiWrapper->callMethod() -> CApiWrapper->callMethod() -> CFrontendApiWrapper->callClientMethod() -> CLocalApiClient->callMethod() -> CTemplate->update() -> CHostGeneral->updateTemplates() -> CHostGeneral::unlinkTemplatesObjects() -> CItem::unlinkTemplateObjects() -> CItem::inherit() -> CItem::inheritChunk() -> CItem::checkInventoryLinks() -> CConfigFile->{closure}() in include/classes/api/services/CItem.php:1412]