Issue with kv Builder - <HighLabel> rule does not override defined <Label> properies

high_label.py

from kivy.lang import Builder
from kivy.uix.label import Label

Builder.load_string('''
<HighLabel>:
    text: 'height dp(40)'
    height: dp(40)
''')


class HighLabel(Label):
    pass

main.py

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.label import Label

from high_label import HighLabel


Builder.load_string('''
<BoxLayout>:
    size: 500, 500

<Label>:
    canvas.before:
        Color:
            rgba: 1,1,1,1
        Rectangle:
            pos: self.pos
            size: self.size

    color: 0,0,0,1
    size_hint: None, None

    height: dp(20)
    text: 'height dp(20)'
''')


class MyApp(App):
    def build(self):
        mainwidget = BoxLayout()
        mainwidget.add_widget(HighLabel())  # ! This label will also have height: dp(20) and text: 'height dp(20)'
        mainwidget.add_widget(Label())
        return mainwidget

if __name__ == '__main__':
    MyApp().run()