MDTextField breaks MDTextFieldHintText and MDTextFieldHelperText if on_focus is added to its class

[marluna2]

Description of the Bug

I don't know why it's like this.
The code should explain it all.

Code and Logs

from kivy.lang import Builder
from kivymd.app import MDApp
from kivymd.uix.textfield import MDTextField

KV = """
BoxLayout: 
    orientation: "vertical"
    padding: "100dp"
    
    WorkingField:
    Widget:
    BrokenField:
    
<WorkingField>
    MDTextFieldHintText:
        text: "This hint text is working"
    MDTextFieldHelperText:
        text: "This helper text is working"
        mode: "on_focus"
        
<BrokenField>
    MDTextFieldHintText:
        text: "This hint text is broken"
    MDTextFieldHelperText:
        text: "This helper text is broken"
        mode: "on_focus"
"""


class WorkingField(MDTextField):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self.bind(focus=self.fixed_on_focus)

    def fixed_on_focus(self, _, __):  # on_focus via self.bind works fine
        pass


class BrokenField(MDTextField):
    def on_focus(self, _, __):  # on_focus via function name breaks the field
        pass


class Example(MDApp):
    def build(self):
        self.theme_cls.primary_palette = "Orange"
        self.theme_cls.theme_style = "Dark"
        return Builder.load_string(KV)


Example().run()

Screenshots

Versions

• OS: Windows 10
• Python: 3.10
• Kivy: 2.3.1
• KivyMD: 2.0.1.dev0