Problem with Virtual Host

[Daniel Benavides]

mrs.

I'm cashing server, if backend page not is virtual host, the cashing 
working.

but the backend page is a virtual host, the cashing not working

I can not modify de webservers.

example
---working

backend default {
     .host = "www.sgi.com";
     .port = "80";
}


---- Not working

backend default {
     .host = "www.omegasystems.cl";
     .port = "80";
}

Please help me