The "strangeness" in the second dump is a result of dumping an object. In the line

my $comment = Tie::IxHash->new(${$comments}{$key});
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$comment is assigned an object reference; it is a thingy that has been blessed as a 'Tie::IxHash'. This is why the dump of $comment looks like

comment: $VAR1 = bless( [
                         ...
                         blah blah blah
                         ...
               ], 'Tie::IxHash' );
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The rest of the 'strangeness' in the second dump consists of other internal data structures in a Tie::IxHash instance.

The real issuse here is using the object correctly. Basically, you want to use the standard TIEHASH interface ot tie the value of your hash to a Tie::IxHash instance. I.e.:

tie (%comments, Tie::IxHash);
warn ("comment " . Dumper($comments{$key}));
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see the perlfunc:tie and perltie documentation for a more in-depth explaination of tied variables