Nuns and monks,
this is a well known feature: if you copy a hash-slice you actually copy references. Following a example snippet:

use strict;
use Data::Dumper;

my %original_hash = (
    'K1' => [
        {'job'   => '_DPL'
        ,'time'  => '_MO_SU_2300'
        }
    ]
);

my @slice_1 =  map {{%$_}} @{$original_hash{'K1'}};
print "original_hash: ", Dumper \%original_hash;
print "slice_1: ", Dumper \@slice_1;

foreach my $item (@slice_1) {
    $item->{'job'} = 'fubar';
}
print "slice_1 after manipulation: ", Dumper \@slice_1;
print "original_hash after manipulation within slice_1: ", Dumper \%or
+iginal_hash;

my @slice_2 = @{ $original_hash{'K1'} };
foreach my $item (@slice_2) {
    $item->{'job'} = 'fubar';
}
print "slice_2 after manipulation: ", Dumper \@slice_2;
print "original_hash after manipulation within slice_2: ", Dumper \%or
+iginal_hash;

___OUTPUT___
original_hash: $VAR1 = {
          'K1' => [
                    {
                      'time' => '_MO_SU_2300',
                      'job' => '_DPL'
                    }
                  ]
        };
slice_1: $VAR1 = [
          {
            'time' => '_MO_SU_2300',
            'job' => '_DPL'
          }
        ];
slice_1 after manipulation: $VAR1 = [
          {
            'time' => '_MO_SU_2300',
            'job' => 'fubar'
          }
        ];
original_hash after manipulation within slice_1: $VAR1 = {
          'K1' => [
                    {
                      'time' => '_MO_SU_2300',
                      'job' => '_DPL'
                    }
                  ]
        };
slice_2 after manipulation: $VAR1 = [
          {
            'time' => '_MO_SU_2300',
            'job' => 'fubar'
          }
        ];
original_hash after manipulation within slice_2: $VAR1 = {
          'K1' => [
                    {
                      'time' => '_MO_SU_2300',
                      'job' => 'fubar'
                    }
                  ]
        };
[download]

Copying into @slice_1 I use map to create new anonymous data. So the problem is solved: I can change the copy without changing the original also.
But is there a better solution to do that? Some sort of "deep copy"?