Negative stride on slice produces wrong result

reverseslice.cxx

#include <vexcl/vexcl.hpp>
#include <vector>
#include <algorithm>

int main() {
  vex::Context ctx(vex::Filter::Env && vex::Filter::Count(1));
  std::cout << ctx << std::endl;

  std::vector<float> v = {
   0, 5,
   1, 4,
   2, 3,
   3, 2,
   4, 1,
   5, 0,
  };
  const std::size_t rows = 6;
  const std::size_t cols = 2;
  vex::vector<float> x(ctx, rows * cols);
  vex::copy(v, x);
  vex::vector<float> z(ctx, rows / 2 * cols);

  vex::slicer<2> slice(vex::extents[rows][cols]);
  std::copy(x.begin(), x.end(), std::ostream_iterator<float>(std::cout, " "));
  std::cout << std::endl;
  z = slice[vex::range(5, -2, 0)][vex::range()](x);
  std::copy(z.begin(), z.end(), std::ostream_iterator<float>(std::cout, " "));
  std::cout << std::endl;
}