I've run into a very odd situation through two different methods now where the results from the zabbix[host,<type>,available] key do not come back with the correct values. The problem this caused was that my triggers based on this particular check for agent/jmx availability were either going off or not going off when they should have.

Here's the first example:

1. Create a host that is monitored by the Zabbix server and make sure values are received correctly (especially zabbix[host,agent,available] should equal "1"). In my case, the host was created through auto-registration. I then added the appropriate templates to it.
2. Bring up a Zabbix proxy and make sure it works correctly with the Zabbix server.
3. Change that created host to be monitored by the newly created Zabbix proxy by editing it's "Server=" value in zabbix_agentd.conf to point to the Zabbix proxy. Restart the agent after making the change.
4. Verify that the host "auto-registers" itself again by changing it's already created profile in the GUI to be monitored by the proxy.
5. Verify that the "Z" icon next to the host in "Configuration"->"Hosts" in the GUI stays green.
6. Go to "Monitoring"->"Latest Data" and verify that information still comes as it should.
7. Watch the value from the zabbix[host,agent,available] key. It will possibly start returning "0" even though the "Configuration"->"Hosts" screen will show the "Z" icon as green.
8. After verifying that the zabbix[host,agent,available] key is returning the wrong value, restart the Zabbix server process.
9. Notice that the zabbix[host,agent,available] key starts returning the correct value.
10. I followed this same process on roughly 50+ servers. At least half of them had this problem occur. The only way to fix it was to restart the Zabbix server process.

The second way that I ran into this is described below:

1. Create a host that is monitored by the Zabbix server and make sure values are received correctly (especially zabbix[host,agent,available] should equal "1"). In my case, the host was created through auto-registration. I then added the appropriate templates to it.
2. Shut the monitored host completely off by doing a hard shut down (using the power button) or disconnect the host from the network.
3. Go to "Monitoring">"Latest Data" and watch the value from the zabbix[host,agent,available] key. It will possibly continue returning "1" even though the "Configuration">"Hosts" screen will show the "Z" icon as red.
4. After verifying that the zabbix[host,agent,available] key is returning the wrong value, restart the Zabbix server process.
5. Notice that the zabbix[host,agent,available] key starts returning the correct value.