nqp::atpos works differently between normal and shaped arrays

gistfile1.txt

use nqp;

sub reverse(\a,\b) {
    my int $elems = a.elems max b.elems;
    my int $last = $elems - 1;
    my Mu $a := nqp::getattr(a,List,'$!reified');
    my Mu $b := nqp::getattr(b,List,'$!reified');
    for ^$elems -> int $i {
        nqp::bindpos(
          $b,
          nqp::sub_i($last,$i),
          nqp::atpos($a,$i)                  # for normal array
#          nqp::decont(nqp::atpos($a,$i))     # for shaped array
        )
    }
    b
}

my @a[5] = ^5;
my @b[5] = ^5;
@a = reverse(@a,@b);
dd @a, @b;