The behaviour you are seeing is actually a feature of Data::Dumper - the $VAR1->{'polished_data'}{'start'} is simply pointing to the first occurrence of what is exactly the same thing. It does this with all references:

use Data::Dumper;
use Time::Piece;

my $tp = gmtime;
my @array = (200,400);

my $data = {
    'one' => {
        'tp' => $tp,
        'array' => \@array,
    },
    'two' => {
        'tp' => $tp,
        'array' => \@array,
    },
};
print Dumper $data;

Output:

$VAR1 = {
  'one' => {
             'array' => [
                          [
                            200,
                            400
                          ]
                        ],
             'tp' => bless( [
                              35,
                              2,
                              2,
                              24,
                              2,
                              '116',
                              4,
                              83,
                              0,
                              1458784955,
                              0
                            ], 'Time::Piece' )
           },
  'two' => {
             'array' => $VAR1->{'one'}{'array'},
             'tp' => $VAR1->{'one'}{'tp'}
           }
};
[download]

To prevent it from doing that you can set Deepcopy:

use Data::Dumper;
$Data::Dumper::Deepcopy = 1;
...

Output:

$VAR1 = {
  'one' => {
             'array' => [
                          [
                            200,
                            400
                          ]
                        ],
             'tp' => bless( [
                              48,
                              10,
                              2,
                              24,
                              2,
                              '116',
                              4,
                              83,
                              0,
                              1458785448,
                              0
                            ], 'Time::Piece' )
           },
  'two' => {
             'array' => [
                          [
                            200,
                            400
                          ]
                        ],
             'tp' => bless( [
                              48,
                              10,
                              2,
                              24,
                              2,
                              '116',
                              4,
                              83,
                              0,
                              1458785448,
                              0
                            ], 'Time::Piece' )
           }
};
[download]