we got a storage performance issue last night, I put all hosts into maintenance, then after the maintenance was over (on 12:00 midnight),
zabbix is keeping on(because there was a half hour escalation) sending false alerts like, see below the agent.ping is up:

Host Name: lb04
Trigger: Zabbix agent on lb04 is unreachable for 10 minutes
Trigger status: PROBLEM
Trigger severity: Warning

Item values:
Agent ping (lb04.nubav.thinkon.net:agent.ping): Up (1)

Event date: 2014.10.24 00:00:00
Original event ID: 10345034

mysql> select * from events where eventid=10345034;
+----------+--------+--------+----------+------------+-------+--------------+----+
| eventid  | source | object | objectid | clock      | value | acknowledged | ns |
+----------+--------+--------+----------+------------+-------+--------------+----+
| 10345034 |      0 |      0 |    28032 | 1414123200 |     1 |            0 |  0 |
+----------+--------+--------+----------+------------+-------+--------------+----+
1 row in set (0.00 sec)