I'm testing ZABBIX1.4.4 using following network

[ZABBIX Server]---------[Router]----------[Windows Vista Client]
(FreeBSD7.0)

ZABBIX Server itself is seem work fine.
it can monitor server itself (zabbix_agentd for FreeBSD) and router box(using SNMP).

But Start to minitoring windows client, I got a probrem.
1. Edit Host Status for windows client "Disable" to "Enable"
2. few seconds past, Windows Client network go to down.
ping from zabbix server to router is reachable.
ping from zabbix server to windows unreach.
ping from windows to router unreach.
3. Edit Host Status for windows "Enable" to "Disable"
THEN ping will be reachable.

zabbix_get from server to client is seems work file.

1. zabbix_get -sWINDOWS-IP" -k"agent.ping"
   1

I read zabbix server and client logs with DebugLevel=4, but i can't find out any infos.

Additionally, I removed router, I got same probrem.