Z-Layer

I have created a big knob for cutoff filter & a tiny knob for resonance.
I want to place the tiny knob in the center of the big knob.

Code:

on init
  make_perfview
  set_script_title("Z-Layer")
  set_ui_height_px(368)
  message("")
  declare $ID
  declare ui_slider $cutoff_filter(0, 1000000)
  $ID := get_ui_id($cutoff_filter)
  set_control_par_str($ID,$CONTROL_PAR_PICTURE,"big_knob")
  set_control_par($ID,$CONTROL_PAR_DEFAULT_VALUE,500000)
  set_control_par($ID,$CONTROL_PAR_Z_LAYER,0)
  declare $cf_x := 250
  declare $cf_y := 108
  move_control_px($cutoff_filter,$cf_x,$cf_y)
  declare ui_slider $resonance_filter(0, 1000000)
  $ID := get_ui_id($resonance_filter)
  set_control_par_str($ID,$CONTROL_PAR_PICTURE,"tiny_knob")
  set_control_par($ID,$CONTROL_PAR_DEFAULT_VALUE,500000)
  set_control_par($ID,$CONTROL_PAR_Z_LAYER,1)
  declare $cfdiff_x := 60
  declare $cfdiff_y := 60
  move_control_px($resonance_filter,$cf_x+$cfdiff_x,$cf_y+$cfdiff_y)
  set_control_help($cutoff_filter,"Cutoff...")
  set_control_help($resonance_filter,"Resonance...")
end on

I can move both knobs independly as expected (it works even without setting the Z-Layer - default 0).

But when I move the mouse cursor to the resonance knob (layer 1), the help text of the cutoff knob (layer 0) will shown instead of the help text of the resonance knob.

I have assumed the Z-Layer feature will help out in this kind of layout.

Is this a bug or am I using the $CONTROL_PAR_Z_LAYER in a wrong way?

 

It might be a bug. But in any case when you have overlapping controls like this, it might make more sense writing a more generalized help text that covers both controls that are stacked, anyways.