public void stopPhysics() {
        if (!isRunning) {
            return;
        }
        if (executor != null) {
            executor.shutdown();
            executor = null;
        }
        pSpace.removeTickListener(this);
        pSpace.destroy();
        isRunning = false;
    }
Stop physics after this state is detached.
jme3-jbullet/src/main/java/com/jme3/bullet/BulletAppState.java