unexpected pass messages in log files

[Andrew Smallbone]

I'm using varnish in a simple system, everything works fine when I
test using curl and web browsers and load testing systems, but when
the content is accessed by our iOS/unity front end, I'm getting "pass"
messages in the log files.  Presumably the HTTP request is subtly
different (It's being logged as HTTP1.1, all requests both working and
not are coming through Amazon ELB - which is terminating the SSL).

Any hints if there's anything I can do with Varnish to see what the
issue is or am I missing something really basic?

varnished (varnish-3.0.3 revision 9e6a70f)
My default.vcl is below - only weirdness is if a specific header isn't
present the request is forwarded to another website, and that header
value is also used in the hash key

sub vcl_recv {
  if (req.http.x-forwarded-for) {
    set req.http.X-Forwarded-For =
    req.http.X-Forwarded-For + ", " + client.ip;
  } else {
    set req.http.X-Forwarded-For = client.ip;
  }
  # ignore AWS/ELB health messages
  if (req.url ~ ".*/health/.*") {
    return (pass);
  }
  // if no header error
  if (!req.http.xxx) {
    error 750 "Moved";
  }
}
sub vcl_error {
  if (obj.status == 750) {
    set obj.response = "Moved Temporarily";
    set obj.http.Location = "http://www.badrequest.com/";
  }
  set obj.status = 302;
  return (deliver);
}
# store results for each header code
sub vcl_hash {
    hash_data(req.url);
    hash_data(req.http.xxx);
    return (hash);
}
sub vcl_fetch {
    set beresp.ttl = 60s;
}
# remove http headers to confuse bad people
sub vcl_deliver {
   remove resp.http.X-Varnish;
   remove resp.http.Via;
   set resp.http.Server = "xxx";
}


regards