Jbullet vs. native bullet, differences for GImpactCollisionShape

I am getting started with physics in jme3. I have a requirement to use the Gimpact code for mesh-mesh collisions. In order to get started I have modified a test case based on code for shooting bullets at a brick tower.
I have tried the code using both the java version of jbullet and the bullet native version. There is a fundamental difference when using GimpactCollsionShape.
I am creating bullets using:
bullet = new Sphere(32, 32, 0.4f, true, false);
bulletCollisionShape = new GImpactCollisionShape(bullet);
This fires bullets OK when using the java verison (jbullet). However, when using the native bullet it merely creates the sphere but it does not have any velocity.

The code is shown below. I have highlighted the relevant section in simpleInitApp()

package testjme3;

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import com.jme3.app.SimpleApplication;
import com.jme3.asset.TextureKey;
import com.jme3.bullet.BulletAppState;
import com.jme3.bullet.PhysicsSpace;
import com.jme3.bullet.collision.shapes.GImpactCollisionShape;
import com.jme3.bullet.collision.shapes.SphereCollisionShape;
import com.jme3.bullet.collision.shapes.CollisionShape;
import com.jme3.bullet.control.RigidBodyControl;
import com.jme3.font.BitmapText;
import com.jme3.input.MouseInput;
import com.jme3.input.controls.ActionListener;
import com.jme3.input.controls.MouseButtonTrigger;
import com.jme3.material.Material;
import com.jme3.math.Vector2f;
import com.jme3.math.Vector3f;
import com.jme3.renderer.queue.RenderQueue.ShadowMode;
import com.jme3.scene.Geometry;
import com.jme3.scene.Mesh;
import com.jme3.scene.shape.Box;
import com.jme3.scene.shape.Sphere;
import com.jme3.scene.shape.Sphere.TextureMode;
import com.jme3.texture.Texture;
import com.jme3.texture.Texture.WrapMode;

public class TestGimpactCollisionShape extends SimpleApplication {

    int bricksPerLayer = 8;
    int brickLayers = 30;

    static float brickWidth = .75f, brickHeight = .25f, brickDepth = .25f;
    float radius = 3f;
    float angle = 0;

    Material mat;
    Material mat2;
    Material mat3;

    private Mesh bullet;
    private CollisionShape bulletCollisionShape;
    
    private Box brick;

    private BulletAppState bulletAppState;

    public static void main(String args[]) {
        TestGimpactCollisionShape f = new TestGimpactCollisionShape();
        f.start();
    }

    @Override
    public void simpleInitApp() {
        bulletAppState = new BulletAppState();
        bulletAppState.setThreadingType(BulletAppState.ThreadingType.PARALLEL);
        stateManager.attach(bulletAppState);
        
        bullet = new Sphere(32, 32, 0.4f, true, false);
        ((Sphere)bullet).setTextureMode(TextureMode.Projected);
        bullet.setDynamic();

// =============================================================================
// This works with jbullet and native bullet        
        bulletCollisionShape = new SphereCollisionShape(0.4f);
// =============================================================================
// This only work with jbullet        
        //bulletCollisionShape = new GImpactCollisionShape(bullet);
// =============================================================================        
        
        brick = new Box(Vector3f.ZERO, brickWidth, brickHeight, brickDepth);
        brick.scaleTextureCoordinates(new Vector2f(1f, .5f));

        initMaterial();
        initTower();
        initFloor();
        initCrossHairs();
        this.cam.setLocation(new Vector3f(0, 25f, 8f));
        cam.lookAt(Vector3f.ZERO, new Vector3f(0, 1, 0));
        cam.setFrustumFar(80);
        inputManager.addMapping("shoot", new MouseButtonTrigger(MouseInput.BUTTON_LEFT));
        inputManager.addListener(actionListener, "shoot");
    }

    private PhysicsSpace getPhysicsSpace() {
        return bulletAppState.getPhysicsSpace();
    }
    private ActionListener actionListener = new ActionListener() {

        public void onAction(String name, boolean keyPressed, float tpf) {
            if (name.equals("shoot") && !keyPressed) {
                Geometry bulletg = new Geometry("bullet", bullet);                                
                bulletg.setMaterial(mat2);
                bulletg.setLocalTranslation(cam.getLocation().clone().add(cam.getDirection()));
                RigidBodyControl bulletNode = new RigidBodyControl(bulletCollisionShape, 2);
                bulletNode.setLinearVelocity(cam.getDirection().mult(50));
                bulletg.addControl(bulletNode);
                rootNode.attachChild(bulletg);
                getPhysicsSpace().add(bulletNode);
            }
        }
    };            
        
    
    public void initTower() {
        double tempX = 0;
        double tempY = 0;
        double tempZ = 0;
        angle = 0f;
        for (int i = 0; i < brickLayers; i++){
            // Increment rows
            if(i!=0)
                tempY+=brickHeight*2;
            else
                tempY=brickHeight;
            // Alternate brick seams
            angle = 360.0f / bricksPerLayer * i/2f;
            for (int j = 0; j < bricksPerLayer; j++){
              tempZ = Math.cos(Math.toRadians(angle))*radius;
              tempX = Math.sin(Math.toRadians(angle))*radius;
              Vector3f vt = new Vector3f((float)(tempX), (float)(tempY), (float)(tempZ));
              // Add crenelation
              if (i==brickLayers-1){
                if (j%2 == 0){
                    addBrick(vt);
                }
              }
              // Create main tower
              else {
                addBrick(vt);
              }
              angle += 360.0/bricksPerLayer;
            }
          }

    }

    public void initFloor() {
        Box floorBox = new Box(Vector3f.ZERO, 10f, 0.1f, 5f);
        floorBox.scaleTextureCoordinates(new Vector2f(3, 6));

        Geometry floor = new Geometry("floor", floorBox);
        floor.setMaterial(mat3);
        floor.setShadowMode(ShadowMode.Receive);
        floor.setLocalTranslation(0, 0, 0);
        floor.addControl(new RigidBodyControl(0));
        this.rootNode.attachChild(floor);
        this.getPhysicsSpace().add(floor);
    }

    public void initMaterial() {
        mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
        TextureKey key = new TextureKey("Textures/Terrain/BrickWall/BrickWall.jpg");
        key.setGenerateMips(true);
        Texture tex = assetManager.loadTexture(key);
        mat.setTexture("ColorMap", tex);

        mat2 = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
        TextureKey key2 = new TextureKey("Textures/Terrain/Rock/Rock.PNG");
        key2.setGenerateMips(true);
        Texture tex2 = assetManager.loadTexture(key2);
        mat2.setTexture("ColorMap", tex2);

        mat3 = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
        TextureKey key3 = new TextureKey("Textures/Terrain/Pond/Pond.jpg");
        key3.setGenerateMips(true);
        Texture tex3 = assetManager.loadTexture(key3);
        tex3.setWrap(WrapMode.Repeat);
        mat3.setTexture("ColorMap", tex3);
    }

    public void addBrick(Vector3f ori) {
        Geometry reBoxg = new Geometry("brick", brick);
        reBoxg.setMaterial(mat);
        reBoxg.setLocalTranslation(ori);
        reBoxg.rotate(0f, (float)Math.toRadians(angle) , 0f );
        reBoxg.addControl(new RigidBodyControl(1.5f));
        reBoxg.setShadowMode(ShadowMode.CastAndReceive);
        reBoxg.getControl(RigidBodyControl.class).setFriction(1.6f);
        this.rootNode.attachChild(reBoxg);
        this.getPhysicsSpace().add(reBoxg);
    }

    protected void initCrossHairs() {
        guiFont = assetManager.loadFont("Interface/Fonts/Default.fnt");
        BitmapText ch = new BitmapText(guiFont, false);
        ch.setSize(guiFont.getCharSet().getRenderedSize() * 2);
        ch.setText("+"); // crosshairs
        ch.setLocalTranslation( // center
                settings.getWidth() / 2 - guiFont.getCharSet().getRenderedSize() / 3 * 2,
                settings.getHeight() / 2 + ch.getLineHeight() / 2, 0);
        guiNode.attachChild(ch);
    }
}