varnishlog can't log every request

[I I]

hi,all. Is anybody find that the varnishlog command can't log every request
.
the problem is here. I set up a varnish and proxy for a website.It
distribute  two server .one set up varnish the other is website server . And
I use the command varnishlog > varnish.log to log the situation about the
Miss and Hit. Even though there many Hit.but the varnish server still
connect to website server . and I capture the network ,the url required from
varnish server to website server can't find from the varnish.log. and I
capture the HTTP in the client . I find the HTTP head  response from server
is directly from the website server .there are nothing signature from the
varnish to mark.
like this:
(Status-Line):HTTP/1.1 200 OK
Date:Fri, 13 Nov 2009 06:39:13 GMT
Server:nginx/0.7.19
ETag:W/"28991-1245029784000"
Last-Modified:Mon, 15 Jun 2009 01:36:24 GMT
Content-Length:28991
Content-Type:image/jpeg
Content-Language:zh-cn
Keep-Alive:timeout=15
Connection:Keep-Alive

here is the normal mark from the varnish
(Status-Line):HTTP/1.1 200 varnish
ETag:W/"4135-1196350806000"
Last-Modified:Thu, 29 Nov 2007 15:40:06 GMT
Content-Type:image/jpeg
Content-Language:zh-cn
Content-Length:4135
Date:Fri, 13 Nov 2009 06:58:19 GMT
Age:1736
Connection:keep-alive
X-Cache:HIT
Via:varnish
server:varnish

why in the file varnishlog which output from the varnishlog ,I can't find
the abnormal url request ? and what's the problems ?
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