New Perl Hate

You don't work with a language every day without building up a "things I hate in language X" list. Well, I have a few hates of Perl, but they've all been fairly well covered in other blogs and cover the usual topics (pre-Moose OO, getting bitten by scalar/list context, etc), however yesterday I came across a new one. Here is a one-liner demonstrating the problem:

$ perl -MData::Dumper -le'@a=qw/a b c/; @foobar = map { $_ } @a[0..7]; print Dumper \@a'
$VAR1 = [
          'a',
          'b',
          'c',
          undef,
          undef,
          undef,
          undef,
          undef
        ];

Fairly obviously, I have created a list with 3 elements in it, tried to slice it with 8 values and assign that to a different list, however when printing the contents of the original list, it has now been padded out to 8 values with undefs. Ok, I thought perhaps doing a slice on a list had that kind of destructive behavior but I had just never noticed it before and had never heard about it previously. So I tried another one-liner to perhaps prove that theory:

$ perl -MData::Dumper -le'@a=qw/a b c/; @foobar = @a[0..7]; print Dumper \@a'
$VAR1 = [
          'a',
          'b',
          'c'
        ];

Nope. Bug? Or expected behavior for some reason that I cannot figure out? This was on Perl 5.8.9