Position problems

learning.kv

<ScatterTextWidget>:
    FloatLayout:
        id: my_flayout
        canvas:
            Color:
                rgba: 0, 1, 0, 1
            Rectangle:
                pos: self.pos
                size: self.size
        Scatter:
            id: my_scatter
            size_hint: None, None
            size: 300, 100
            canvas.after:
                Color:
                    rgb: 1, 0, 1
                Rectangle:
                    pos: self.pos
                    size: self.size

main.py

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout


class ScatterTextWidget(BoxLayout):
    pass


class LearningApp(App):
    def build(self):
        root_widget = ScatterTextWidget()

        scat = root_widget.ids['my_scatter']
        fllt = root_widget.ids['my_flayout']

        print(scat.center)
        print(fllt.center)

        scat.center = fllt.center

        print(scat.center)
        print(fllt.center)

        return root_widget


if __name__ == "__main__":
    LearningApp().run()