explanation

So... if you run the very-broken script, everything works properly, both running the version of
very-broken-combinations from core and the indentical but for name copy very-broken-combinations-local
here.  If you run very-broken-combinations from the REPL, it will fail:

  > very-broken-combinations(3,2)
  ([9 10] [9 10] [9 10] [9 10] [9 10])
  
The original combinations bug also occurred when running combinations.t, which is how I discovered it.
I haven't tried setting up a test file for very-broken-combinations.

very-broken

sub very-broken-combinations-local($n, $k) {
    my @result;
    my $value = 1;

    gather for 0..4 {
        for 0..1 {
            @result[$_] = $value++;
        }
        take @result;
    }
}

say very-broken-combinations(3,2);
say very-broken-combinations-local(3,2);