F5 LTM (VE) - KeepAlive even if real server close connection

[root@ve10:Active] config  ssldump -Aed -nni 0.0 port 80
New TCP connection 1: 172.28.19.251(46046) <-> 172.28.19.79(80)
1346770377.3176 (0.0011)  C>S
---------------------------------------------------------------
GET / HTTP/1.1
User-Agent: curl/7.15.5 (i686-redhat-linux-gnu) libcurl/7.15.5 OpenSSL/0.9.8b zlib/1.2.3 libidn/0.6.5
Host: 172.28.19.79
Accept: */*
Connection: keep-alive

---------------------------------------------------------------

New TCP connection 2: 172.28.19.251(46046) <-> 1.1.1.1(80)
1346770377.3177 (0.0000)  C>S
---------------------------------------------------------------
GET / HTTP/1.1
User-Agent: curl/7.15.5 (i686-redhat-linux-gnu) libcurl/7.15.5 OpenSSL/0.9.8b zlib/1.2.3 libidn/0.6.5
Host: 172.28.19.79
Accept: */*
Connection: keep-alive

---------------------------------------------------------------

New TCP connection 3: 200.200.200.10(46046) <-> 200.200.200.101(80)
1346770377.3185 (0.0007)  C>S
---------------------------------------------------------------
GET / HTTP/1.1
User-Agent: curl/7.15.5 (i686-redhat-linux-gnu) libcurl/7.15.5 OpenSSL/0.9.8b zlib/1.2.3 libidn/0.6.5
Host: 172.28.19.79
Accept: */*
Connection: keep-alive

---------------------------------------------------------------

1346770377.3197 (0.0011)  S>C
---------------------------------------------------------------
HTTP/1.1 200 OK
Connection: close
Date: Tue, 04 Sep 2012 06:59:04 GMT
Server: Microsoft-IIS/6.0
Set-Cookie: CFID=26760493;expires=Thu, 04-Oct-2012 06:59:04 GMT;path=/
Set-Cookie: CFTOKEN=85662049;expires=Thu, 04-Oct-2012 06:59:04 GMT;path=/
Content-Type: text/html; charset=UTF-8

---------------------------------------------------------------

3    1346770377.3197 (0.0000)  S>C  TCP FIN
1346770377.3197 (0.0020)  S>C
---------------------------------------------------------------
HTTP/1.1 200 OK
Connection: close
Date: Tue, 04 Sep 2012 06:59:04 GMT
Server: Microsoft-IIS/6.0
Set-Cookie: CFID=26760493;expires=Thu, 04-Oct-2012 06:59:04 GMT;path=/
Set-Cookie: CFTOKEN=85662049;expires=Thu, 04-Oct-2012 06:59:04 GMT;path=/
Content-Type: text/html; charset=UTF-8
Transfer-Encoding: chunked

0

---------------------------------------------------------------

2    1346770377.3197 (0.0000)  S>C  TCP FIN
1346770377.3198 (0.0021)  S>C
---------------------------------------------------------------
HTTP/1.1 200 OK
X-Cnection: close
Date: Tue, 04 Sep 2012 06:59:04 GMT
Server: Microsoft-IIS/6.0
Set-Cookie: CFID=26760493;expires=Thu, 04-Oct-2012 06:59:04 GMT;path=/
Set-Cookie: CFTOKEN=85662049;expires=Thu, 04-Oct-2012 06:59:04 GMT;path=/
Content-Type: text/html; charset=UTF-8
Transfer-Encoding: chunked

0

---------------------------------------------------------------

2    1346770377.3198 (0.0000)  C>S  TCP FIN
3    1346770377.3198 (0.0000)  C>S  TCP FIN
1    1346770377.3215 (0.0017)  C>S  TCP FIN
1    1346770377.3215 (0.0000)  S>C  TCP FIN