I already found some diffirences with the HEAD request from Curl or from our content switch:

css:
stmycew01.hf.info.nl - - [21/Sep/2009:13:46:10 +0200] "HEAD /web/MYLER.htm HTTP/1.1" 200 - "-" "Mozilla/4.06 [en] (WinNT; I)"

curl head 1.1 test:
10.101.111.112 - - [21/Sep/2009:13:47:08 +0200] "HEAD /web/MYLER.htm HTTP/1.1" 404 - "-" "curl/7.19.6 (i386-pc-win32) libcurl/7.19.6 zlib/1.2.3"

curl head 1.0 test:
10.101.111.112 - - [21/Sep/2009:13:47:31 +0200] "HEAD /web/MYLER.htm HTTP/1.0" 404 - "-" "curl/7.19.6 (i386-pc-win32) libcurl/7.19.6 zlib/1.2.3"



c:\tools>curl -I -1 http://stbizzw01:80/web/MYLER.htm
HTTP/1.1 404 Not Found
Date: Mon, 21 Sep 2009 11:47:08 GMT
Content-Type: text/html; charset=UTF-8
Connection: close


c:\tools>curl -I -0 http://stbizzw01:80/web/MYLER.htm
HTTP/1.1 404 Not Found
Date: Mon, 21 Sep 2009 11:47:31 GMT
Content-Type: text/html; charset=UTF-8
Connection: close


I also think it is the backend but I can not see what is different?
I also find out that the css request are looking to coming internally from the CMS (or are rerouted through the CMS).