I'm having a situation when the value for an item is displayed incorrectly in monitoring > overview > data (thus triggering the alert), but when I check "500 latest values" I see that it's actually correct. See the attachments.
This started when I transferred my Zabbix 1.8.1/Postgresql 8.4 installation to Zabbix 1.8.16/Postgresql 9.2 (another server). After spending a day on this problem I decided to try Zabbix 2.0.5 (I'm using official Centos repos). It persisted. The item is "numeric unsigned", "decimal", "zabbix agent (active)".
The weirdest thing is that the same item works fine at another group of hosts.