Also, one of Apache::Registry's shortcomings was a confusing and somewhat incomplete approach to sharing variables among sessions. Since the code is cached, the variables aren't automatically re-initialized each time the script is run. This might solve your problem:

  my $foo ;           ## usually ok in perl
  my $foo = undef ;   ## an Apache::Registry requirement?
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If you're not committed to Apache::Registry. Consider an alternative. Also, the mod_perl mailing list: http://perl.apache.org

Oh, and to answer your other question...

$VAR1 = {
          'MOD_PERL_API_VERSION' => 2,
          'MOD_PERL' => 'mod_perl/2.0.4'
        };
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In Apache config, though:

PerlResponseHandler ModPerl::Registry

Our code is "not mod_perl safe", so we were told to use Registry to work around that.

Our code is "not mod_perl safe", so we were told to use Registry to work around that.

Yup, Registry is used to run .cgi's under mod_perl but isn't a cure-all, it won't magically make sure you're using CGI.pm correctly or that you're Coping with Scoping -- see (this which you probably already saw) for some issue CGI to mod_perl Porting. mod_perl Coding guidelines and tweak your code

That patch, Apache::ChildExit, is still on CPAN. I don't have much time to consider your question. But I generally post this answer when I see problems with Apache::Registry.

How would this cause data duplication or stale data or data from previous session/request leaking through to a new one? Cause it wouldn't you know, its pretty much guaranteed to have nothing to do with it