It is possible that the following appears in the logs:

30309:20131021:183031.085 temporarily disabling Zabbix agent checks on host [MyHost]: host unavailable
30308:20131021:183031.086 temporarily disabling Zabbix agent checks on host [MyHost]: host unavailable

When we make a host unavailable, we set this host's triggers to unknown and generate corresponding internal events. So one of the problems with the above is that multiple such internal events are generated.