Undesired/Unexpected Compiler-Magic with Eigen and Ternary Operator

The following code unexpectedly assigns (0, -1, 0) instead of (0, 1, 0) as intended. Why? Any ideas?

#include <Eigen/Dense>

int main()
{
  const bool useFirst = false;

  // This is the original use-case.
  const Eigen::Vector3d vect1
    = useFirst ? -Eigen::Vector3d::UnitZ() : Eigen::Vector3d::UnitY();

  // This version is somewhat simplified, but exhibits the same problem.
  const Eigen::Vector3d unitZ(0.0, 0.0, 1.0), unitY(0.0, 1.0, 0.0);
  const Eigen::Vector3d vect2 = useFirst ? -unitZ : unitY;

  // FYI, this version does not compile (?).
  // const Eigen::Vector3d vect3
  //   = useFirst ? -unitZ : Eigen::Vector3d::UnitY();
}