take problems on JVM

gistfile1.txt

    sub ROLLPICKGRABN(                                        # N times
      $self, $count, @pairs is rw, :$keep
    ) is hidden_from_backtrace {
        my Int $total = $self.total;
        my Int $rand;
        my Int $seen;
        my int $todo = ($keep ?? $count !! ($total min $count)) + 1;

        gather {
            while $todo = $todo - 1 {
                $rand = $total.rand.Int;
                $seen = 0;
                for @pairs -> $pair {
                    next if ( $seen += $pair.value ) <= $rand;

                    take $pair.key;
                    last if $keep;

                    $pair.value--;
                    $total = $total - 1;
                    last;
                }
            }
        }
    }

Seems to happen in take

Exception in thread "main" org.perl6.nqp.runtime.UnwindException
	at org.perl6.nqp.runtime.ThreadContext.<init>(ThreadContext.java:119)
	at org.perl6.nqp.runtime.GlobalContext.getCurrentThreadContext(GlobalContext.java:333)
	at org.perl6.nqp.runtime.GlobalContext.<init>(GlobalContext.java:248)
	at org.perl6.nqp.runtime.CompilationUnit.enterFromMain(CompilationUnit.java:56)
	at perl6.main(gen/jvm/main.nqp)