Which environment variables are you talking about? It's possible that, for some env. variables, like HTTP_REFERER, they're not getting set because you're invoking the new window in a different way than, say, when a user clicks on a link. Browsers often only send the HTTP_REFERER variable, for example, when you've actually clicked on a link.

So, I guess the question would be: are *none* of the env. variables getting set--which would be a bit odd and would indicate some trouble, possibly--or just the specific ones that you're using?

for my $key ($keys %ENV) {
    print $key, ": ", $ENV{$key}, "<br>\n";
}
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In case you haven't tried seeing which ones are being set already.