mod_perl? Don't use "global" lexicals in mod_perl Registry script. Had you turned on warnings, you would have gotten one. mod_perl wraps your script in a function, so you basically get

sub mod_perl_wrapper {
   ##### Begining of script #####
   use strict;
   use warnings;

   my $global = $_[0];   # Say some value from the request.

   sub foo {
      # Warms 'Variable "$global" will not stay shared'
      print("$global\n");
   } 

   foo();

   ##### End of script #####
}

mod_perl_wrapper(4);  # First request prints "4"
mod_perl_wrapper(5);  # Subsequent requests also prints "4"
[download]

Use a package variable instead.

sub mod_perl_wrapper {
   ##### Begining of script #####
   use strict;
   use warnings;

   local our $global = $_[0];   # Say some value from the request.

   sub foo {
      print("$global\n");
   } 

   foo();

   ##### End of script #####
}

mod_perl_wrapper(4);  # 1st request prints "4"
mod_perl_wrapper(5);  # 2nd request prints "5"
[download]

I almost mentioned this earlier. I can't believe you went through all this trouble rather than turning on warnings. Even if you don't normally use them for whatever reason, adding use strict; and use warnings; is the first thing you should do when you have a problem you can't explain.