Zabbix server and proxy continue to retrieve values from IPMI sensors even if the machine is shutdown state. ipmitools return "na" for such case.
IPMI device return values with sensor status but Zabbix doesn't check the status.
So Zabbix retrieve values from not working IPMI sensors (i.e. CPU temperature is 50 degree from stopped machine)
According to IPMI 2.0 specification, IPMI client should check sensor status before getting value. IPMI item should be not-supported state in that case.