Extra layer of nesting added after return

overwrite-array-from-sub.p6

sub modify-copy-and-return(@a is copy, @b is copy) {
  my @buffer;
  @buffer.append: @a; 
  @buffer.append: @b;

  @buffer.push: [1,2];

  dd @buffer;
  # Array @buffer = [[1, 2], [3, 4], [3, 4], [5, 6], [1, 2]]
  True, @buffer;
}

my @a = [1,2],[3,4];
my @b = [3,4],[5,6];

my $should-continue = False;
my @buffer;
($should-continue, @buffer) = modify-copy-and-return(@a, @b);

dd $should-continue;
dd @buffer;
# Array @buffer = [[[1, 2], [3, 4], [3, 4], [5, 6], [1, 2]],]