in reply to Strange Behaviour of Two Hashes

Something is awry with your particular Perl setup, I think. I ran your code verbatim, and got the following output: 

$VAR1 = {
          'S1' => 'C-D',
          'S2' => 'C-D',
          'S4' => 'CID',
          'S3' => 'CAD'
        };
From LOOP
$VAR1 = {
          'S1' => 'C-D',
          'S2' => 'C-D',
          'S4' => 'CID',
          'S3' => 'CAD'
        };

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Is something wrong with this? For reference: 

This is perl, v5.8.6 built for MSWin32-x86-multi-thread

[download]

The Eightfold Path: 'use warnings;', 'use strict;', 'use diagnostics;', perltidy, CGI or CGI::Simple, try the CPAN first, big modules and small scripts, test first.

In Section Seekers of Perl Wisdom