ListBox method set_focus_valign always set align to top about urwid HOT 1 OPEN

import urwid

palette = [
    ('normal', 'light gray', 'black', '', "light gray", "black"),
    ('focused', 'light blue', 'black', '', "light blue", "black"),
]

class Ui:
    def __init__(self):
        self.header = urwid.Text('Hello World!')
        layout = [
            urwid.AttrMap(
                urwid.Padding(urwid.SelectableIcon(str(n)), left=1, right=1),
                attr_map={}, focus_map={None: "focused"}
            )
            for n in range(100)
        ]
        self.listbox = urwid.ListBox(layout)
        self.statusbar = urwid.Text('statusbar', align='right')
        self.main_frame = urwid.Frame(self.listbox)
        self.main_frame.set_footer(self.statusbar)
        self.mainloop = urwid.MainLoop(
            self.main_frame,
        palette=palette, unhandled_input=self.unhandled_input
        )

    def unhandled_input(self, key):
        if key in ('q', 'Q'):
            raise urwid.ExitMainLoop()
        elif key in ['G']:
            self.listbox.set_focus(2)
            self.listbox.set_focus_valign('bottom')
        elif key in ['0']:
            self.listbox.set_focus(5)
        elif key in ['1']:
            self.listbox.set_focus_valign('top')
            self.listbox._invalidate()
        elif key in ['2']:
            self.listbox.set_focus_valign('middle')
            self.listbox._invalidate()
        elif key in ['3']:
            self.listbox.set_focus_valign('bottom')
            self.listbox._invalidate()

if __name__ == '__main__':
    ui = Ui()
    ui.mainloop.run()