Haversine closest point is incorrect, at least at high lattitudes?

[jodavaho]

Please correct me if my assumptions or test is incorrect.

use geo::prelude::*;
use geo::point;
use approx::assert_abs_diff_eq;
fn main() {
    // Make sure midpoint returned when at high latitudes
    use geo::Geodesic;
    let pt_a = point!(x: 0.0, y: 80.0);
    let pt_b = point!(x: 179.99, y: 80.0);
    let ln = geo::Line::new(pt_a, pt_b);
    let d = Geodesic::distance(pt_a, pt_b);
    let midpoint = Geodesic::point_at_ratio_between(pt_a, pt_b, 0.5);
    eprintln!("the midpoint is {:?}", midpoint);
    let closest_point = {
        let closest_res = ln.haversine_closest_point(&midpoint);
        use geo::Closest::*;
        match closest_res {
            Intersection(p) => p,
            SinglePoint(p) => p,
            Indeterminate => {
                panic!("Indeterminate");
            }
        }
    };
    assert_abs_diff_eq!(closest_point.y(), midpoint.y(), epsilon = 1e-6);
    assert_abs_diff_eq!(closest_point.x(), midpoint.x(), epsilon = 1e-6);
}

The returned closest point is neither the input point or on the geodesic line.

again, please correct me if I've done something incorrect here.