Modify the value of model.site_pos during simulation, the value of data.site_xpos does‘t update accordingly

[BowenFF]

When the simulation is running, I want to modify the pose of a site. I use the following code:

int site_id = get_site_id(site_name);
    if (site_id != -1) {
        Eigen::VectorXd translation_vec = DQ_robotics::vec3(DQ_robotics::translation(pose));
        model_->site_pos[3*site_id+0] = translation_vec[0];
        model_->site_pos[3*site_id+1] = translation_vec[1];
        model_->site_pos[3*site_id+2] = translation_vec[2];

        DQ rotation_dq = DQ_robotics::rotation(pose);
        rotation_dq = DQ_robotics::normalize(rotation_dq);  
        
        model_->site_quat[4*site_id+0] = rotation_dq.q(0);  // w
        model_->site_quat[4*site_id+1] = rotation_dq.q(1);  // x
        model_->site_quat[4*site_id+2] = rotation_dq.q(2);  // y
        model_->site_quat[4*site_id+3] = rotation_dq.q(3);  // z
        
        mj_forward(model_, data_);

After that, I found that the value of model.site_pos was successfully updated, but the value of data.site_xpos did not change accordingly. Why is this happening?