When changing an existing item type from to trapper, previous item update interval value is kept in db.
When creating a new trapper item, hidden item update interval is set in db to 60 behind the scenes.
It leads to wrong calculation of NVPS value in zabbix status:

config.inc.php:
691 $sql = 'SELECT sum(1.0/i.delay) as qps '.
692 ' FROM items i,hosts h '.
693 ' WHERE i.status='.ITEM_STATUS_ACTIVE.
694 ' AND i.hostid=h.hostid '.
695 ' AND h.status='.HOST_STATUS_MONITORED.
696 ' AND i.delay<>0';
697 $row = DBfetch(DBselect($sql));

As you can see, trapper items are included in calculation and able to drastically distort the NVPS value.

Possible resolutions:
1) Forcible reset of item update interval value to 0 on trapper item edit/create
2) Ignore trapper items in NVPS calculation
3) Ability to manually specify prognosed update interval in trapper item properties (setting this interval to 0 removes item from NVPS calculation)