Incorrect evaluation of Ref

Assigning the result of bottomRows to Eigen::Ref does not seem to work correctly:

#include <iostream>
#include <Eigen/Dense>

int main() {
  constexpr int num_rows = 3;
  constexpr int num_columns = 4;
  Eigen::MatrixXd y = Eigen::MatrixXd::Random(num_rows, num_columns);

  constexpr int num_bottom_rows = 1;
  const Eigen::Ref<const Eigen::Matrix<double, num_bottom_rows, num_columns>> z =
      y.bottomRows(num_bottom_rows);

  // These should be the same but are not.
  std::cout << y.bottomRows(num_bottom_rows) << '\n'
            << z << '\n';
}

Example output:

$ clang++ -std=c++17 -I/home/luke/repos/eigen ./eigen_ref_mwe.cpp -o ./eigen_ref_mwe; ./eigen_ref_mwe
 0.566198 -0.604897 -0.444451  0.257742
 0.566198   0.59688  0.823295 -0.604897

I've tracked this down on the following commit on the 3.3 branch: 7b93328b

The parent commit 6adb70d3 does not exhibit the issue.

fyi @ggael @chhtz @rmlarsen1 eigen_ref_mwe.cpp