Looks like the problem was in Frontier::Responder itself. I made these changes:

plankton@ubuntu:/usr/local/share/perl/5.10.1/Frontier$ diff Responder.
+pm Responder.pm_old 
19,20d18
< #plankton I put it back
< use CGI;
53,55c51
< #    my $request = get_cgi_request();
< my $cgi    = new CGI;
< my $request    = $cgi->param('POSTDATA');
---
>     my $request = get_cgi_request();
[download]

and now my test script works.