calculated item referencing an unsupported item says the item is not found

Suppose we have a calculated item that references another item. Everything goes well until that another item becomes unsupported. In this case, the calculated item becomes unsupported, too, with the error message similar to "Cannot evaluate function [last()]: item [Zabbix server:trapper.item] not found". This is misleading, because the item exists and it used to work well.