Changing the event in test_listen_and_simulate() to EventType::Wheel{delta_x: 0, delta_y: -1} (or delta_y: 1) gives a test failure because simulating wheel events does nothing! Print-debugging indicates that listening for scroll events with a hardware mouse works as expected. And finally, I wrote a snippet with the buggy behavior.

fn main() {
    loop {
        simulate(&EventType::Wheel {
            delta_x: 0,
            delta_y: -1,
        }).unwrap();
        std::thread::sleep(std::time::Duration::from_millis(100))
    }
}

details: Windows 10 version 1903, rdev master branch