I have trigger with expression "{Template SNMP Interfaces:ifOperStatus[

].diff(0)}=1" with unset "Multiple PROBLEM events generation" checkbox.
It works good on most cases.
Sometimes it generates two events (one and next after a minute) on single interface change, with the same

.
Zabbix configuration was not changed that time.
Attached screenshot of event history related to this one trigger (filtered by triggerid).
Item history from that period:

mysql> select from_unixtime(clock), value from history_uint join items using (itemid) join hosts using (hostid) where key_ = 'ifOperStatus[1:20]' and host = 'ua-ix-670-2-1' and clock>unix_timestamp('2013-10-16 00:05:00') and clock<unix_timestamp('2013-10-16 00:25:00') order by clock;
---------------------------+

---------------------------+

---------------------------+
20 rows in set (0.03 sec)