I believe you want to change sub_c so that it just looks like:

sub sub_c
{
    my %hash1c = @_;

    print "sub_c arguments: " . Dumper \%hash1c;
}
[download]

Here's the whole script cleaned up a little:

[05:25][nick:~/monks]$ cat 1134864.pl
#! perl
use strict;
use warnings;
use feature qw/ say /;
use Data::Dumper;

sub sub_b {
  my %hash1b;
  $hash1b{'key1'} = 1;

  say 'calling sub_c from sub_b';
  sub_c( %hash1b );
}

sub sub_c {
  my %hash1c = @_;
  say 'sub_c arguments: ' . Dumper \%hash1c;
}

say 'calling sub_b';
sub_b();

my %hash1a;
$hash1a{'key1'} = 1;

say 'calling sub_c directly';
sub_c( %hash1a );

__END__
[download]

[05:25][nick:~/monks]$ perl 1134864.pl
calling sub_b
calling sub_c from sub_b
sub_c arguments: $VAR1 = {
          'key1' => 1
        };

calling sub_c directly
sub_c arguments: $VAR1 = {
          'key1' => 1
        };
[download]