If you go to "Configuration" -> "Maps" and modify an existing map element of type "host" on a map and change the element from type "Host" to type "Image" and back to type "Host" and save the map element, you will get the following error below:

No host with hostid=[0]
Looking at table "sysmaps_elements", I can see that the map element I was modifying, the field "elementid" is getting replaced by "0" and loosing the original "elementid" number.

http://www.zabbix.com/forum/showpost.php?p=42438&postcount=10