I'm pretty sure that the browser is to blame, not CGI.

Take a look at the raw POST request, for example with a sniffer like wireshark. If the browser doesn't send the params, there's now way CGI.pm can deliver you the values.

Update I tested it with a HTML form which contains only ids and no names, and this is what went over the wire:

OST / HTTP/1.1

Host: moritz

User-Agent: Mozilla/5.0 (X11; U; Linux i686; de-DE; rv:1.8.1.14) Gecko
+/20080404 Iceweasel/2.0.0.14 (Debian-2.0.0.14-0etch1)

Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9
+,text/plain;q=0.8,image/png,*/*;q=0.5

Accept-Language: de-de,de;q=0.8,en-us;q=0.7,en;q=0.5,en-gb;q=0.3,nb;q=
+0.2

Accept-Encoding: gzip,deflate

Accept-Charset: UTF-8,*

Keep-Alive: 300

Connection: keep-alive

Referer: http://moritz/de/bar

Content-Type: application/x-www-form-urlencoded

Content-Length: 0
[download]

You can see from teh Content-Length that no form data is actually submitted - bad luck for you. (Note that my test HTML form didn't have a xhtml strict DTD, so it might work for some browsers with that DTD. But I don't think it works with the broken browsers that >50% of all people use.)