Perl: simple foreach on hash hands mixed results?

Question

Possible Duplicate:
What decides the order of keys when I print a Perl hash?

Say I got a simple script to list the contents of a hash from a book:

my %hash = ("a" => 1, "b" => 2, "c" => 3, "d" => 4);

for my $i (%hash) {
    print $i . "\n";
}

On one computer it lists: c 3 a 1 b 2 d 4

But on another it has it proper (in order): a 1 b 2 c 3 d 4

Why does it do this? does the foreach list it randomly or is it some random bug? My current (the c-a-b-d one is running Perl 5.10.1 the other 5.6?)