CylinderCollisionShape HalfExtents -> Y?

Playing around with CollisionShapes I noticed that the y-float of the vector you give a CylinderCollisionShape seems not to have any meaning.
So while changing the x- or z-float of that vector does make a change of the CollisionShape, the y-param does not.
public class Main extends SimpleApplication

BulletAppState bulletAppState = new BulletAppState();
CylinderCollisionShape cylinderCollisionShape = new CylinderCollisionShape(new Vector3f(1, 20, 1));
Geometry geom = new Geometry("Box", new Box(1, 1, 1));

public static void main(String[] args)
    Main app = new Main();

public void simpleInitApp()
    cam.setLocation(new Vector3f(-10, 10, -10));
    geom.setMaterial(new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md"));
    geom.addControl(new RigidBodyControl(cylinderCollisionShape, 0));
    cam.lookAt(geom.getWorldTranslation(), Vector3f.UNIT_Y);


Changing the Shape to
[java]new CylinderCollisionShape(new Vector3f(1, 40, 1));[/java]
[java]new CylinderCollisionShape(new Vector3f(1, 0, 1));[/java]
or whatever does not change anything.

Yes, this is correct.

So it is supposed to be this way?
If so, why making the parameter a Vector3, if a Vector2 would do?

So after searching the web a little a found a forum-post (bullet-forum) where “non-circular”-cylinder shapes are mentioned and after skimming this wikipedia-article -> I guess the CylinderCollisionShape is circular, meaning that both radii are the same size anyway, simply ignoring the y-float.
Still it is a little confusing that a parameter is obiously needless…
I could be wrong though since my english isn’t the best…