Move circle on top of a demo (music)

I don’t really understand the principle of LVGL yet.
The demo lv_demo_music() I got so far to run.

Now I’m trying to move a red circle on top of this demo on a touch interrupt, see code below (this is just for testing purposes). Unfortunately this does not work properly, see video-link below. Where does this effect come from, or what did I get wrong here?

static lv_obj_t * my_Cir;
uint16_t xpos1=0, ypos1=0;


void setup()

  //static lv_obj_t * my_Cir = lv_obj_create(lv_scr_act());
  my_Cir = lv_obj_create(lv_scr_act());
  lv_obj_set_scrollbar_mode(my_Cir , LV_SCROLLBAR_MODE_OFF);
  lv_obj_set_size(my_Cir , 42, 42);
  lv_obj_set_pos(my_Cir, 100, 100);
  lv_obj_set_style_bg_color(my_Cir , lv_palette_lighten(LV_PALETTE_RED, 3), 0);
  lv_obj_set_style_radius(my_Cir , LV_RADIUS_CIRCLE, 0);


void loop()
  lv_timer_handler(); /* let the GUI do its work */
  delay( 5 );  

           // move circle  
            lv_obj_set_pos(my_Cir, xpos1++, ypos1++);