Steps to reproduce:
Update Template LLD dependent item

Result:

Undefined index: master_itemid [disc_prototypes.php:453 ? CFrontendApiWrapper->update() ? CApiWrapper->__call() ? CFrontendApiWrapper->callMethod() ? CApiWrapper->callMethod() ? CFrontendApiWrapper->callClientMethod() ? CLocalApiClient->callMethod() ? call_user_func_array() ? CItemPrototype->update() ? CItemPrototype->inherit() ? CItemGeneral->inheritDependentItems() in include/classes/api/services/CItemGeneral.php:1634]

See screenshot...