global position and size alter after awhile

Hi, dear godot master

I am trying to do Making Buttons with animations in godot 4.0.2

and what confuse me it's:

node global position and size alter after awhile, it makes:

1. If I dont await 0.01second.finished in _ready() virtual method,

selector will appear in wrong position at first

2. if I dont set pivot_offset in script, no matter what's the value in inspector, it turns to 0,0

it's a bug or what I doing wrong?

extends Control

@export var bg:ButtonGroup

@onready var icon: Sprite2D = $Icon

@onready var v_box_container: VBoxContainer = $VBoxContainer

@onready var buttons := bg.get_buttons()

# Called when the node enters the scene tree for the first time.

func _ready() -> void:

 await create_tween().tween_interval(0.1).finished

 for i in buttons:

  i.mouse_entered.connect(i.grab_focus)

  i.focus_entered.connect(movetobutton.bind(i))

  i.focus_exited.connect(moveaway.bind(i))

  i.pressed.connect(clickbutton.bind(i))

  i.pivot_offset = i.size/2

 buttons[0].grab_focus()

# Called every frame. 'delta' is the elapsed time since the previous frame.

func _process(delta: float) -> void:

 pass

func movetobutton(button:Button):

 var tween = create_tween()

 tween.tween_property(icon,"position",button.global_position,0.2).from_current()

 tween.tween_property(button,"scale",Vector2.ONE * 1.1,0.15).from_current()

func moveaway(button:Button):

 var tween = create_tween()

 tween.tween_property(button,"scale",Vector2.ONE,0.15).from_current()

func clickbutton(button:Button):

 var t = create_tween().set_parallel(true).set_trans(Tween.TRANS_ELASTIC)

 t.tween_property(button,"scale",Vector2.ZERO,0.3).from_current()

 t.tween_property(button,"rotation",deg_to_rad(-40),0.3).from(deg_to_rad(40))

 await t.finished

 t = create_tween().set_parallel(true).set_trans(Tween.TRANS_ELASTIC)

 t.tween_property(button,"scale",Vector2.ONE,0.3).from_current()

 t.tween_property(button,"rotation",deg_to_rad(0),0.3).from_current()