Lighttpd

I want to use lighty as load-balancer . so I use light v1.5.0 with mod_proxy_core and mod_proxy_backend_http.
But I find lighty use too many connections back to backend and do not use keep-alive mod(I find lighty send FIN to backends).
so who can give me some hints on this? I use light v1.4.20 with mod_proxy and It doesnt work too.

here is my conf files(lighty v1.5):

#start here
server.modules = ( "mod_proxy_core", "mod_proxy_backend_http", "mod_status" )

server.document-root = "/var/www"
server.port = 80
server.max-keep-alive-requests = 16
#server.max-read-idle = 10
server.errorlog = "/data/proclog/log/debug.log"

server.max-fds = 2048
server.network-backend = "linux-aio-sendfile"
#server.network-backend = "linux-sendfile"
server.event-handler = "linux-sysepoll"
server.max-worker = 4

proxy-core.protocol = "http"
proxy-core.max-pool-size = 20
proxy-core.max-keep-alive-requests = 200
proxy-core.balancer = "carp"
proxy-core.backends = ("192.168.3.67:80", "192.168.3.54:80", "192.168.3.61:80")
#config file end

And I find a triger who "recycle" the backend connect is called in main loop of mod_proxy_core every time to set the connect to be useless(IDLE->CLOSED). Am I right?