G'day LanX,

I can't reproduce this with v5.18.1 (darwin-thread-multi-2level):

$ perl -MData::Dumper -e ' %h1=(3 => 1, 5 => 1, 10 => 3 ); @l=%h2=reve
+rse %h1; print Dumper \@l,\%h2'
$VAR1 = [
          1,
          '3',
          3,
          '10'
        ];
$VAR2 = {
          '1' => '3',
          '3' => '10'
        };
$ perl -MData::Dumper -e ' %h1=(3 => 1, 5 => 1, 10 => 3 ); %h4=%h3=%h2
+=reverse %h1; print Dumper \%h2,\%h3,\%h4'
$VAR1 = {
          '1' => '3',
          '3' => '10'
        };
$VAR2 = {
          '1' => '3',
          '3' => '10'
        };
$VAR3 = {
          '1' => '3',
          '3' => '10'
        };
[download]

In v5.18.0, there were changes to hashes (see perl5180delta: Hash overhaul). This meant that running these one-liners (potentially) produced different results each time. I ran these a few times: I got different results as expected but none reproduced what you're seeing. Here's some examples of this: