We have "Template ICMP Ping" in the default installation of Zabbix with three items: icmpping, icmppingsec, and icmppingloss. The time these items will be checked is calculated based on their item ID, so most probably these items will be scheduled for a check at times T, T+1, and T+2.
Now, suppose Zabbix server only has one pinger running. It will take the first item at time T and process it. Processing will take around 3 seconds, so the next time it looks into the queue it is going to process the other two items. So in order to obtain values for a single host two passes are needed.
It would be nice to check all three items with a single fping invocation. The easiest way of doing this is scheduling a check based on their interface ID, rather than on item ID.