Why does holding down the 'X' button in a toplevel stop execution of main window in tkinter?

I have a program that needs to open Toplevel windows except the main Tk() window in tkinter. In the main window I have a Scale widget which is updated every 100 miliseconds with the after call. However in a state where the Toplevel window is open and the scale is updated when I press down the 'X' button in the Toplevel window the Scale stops moving.

This is my code:

from tkinter import Tk, Toplevel, Scale

root = Tk()

slider = Scale(root, orient='horizontal')
slider.pack()
num = 0


def main():
    global num
    slider.set(num)
    num += 1
    slider.after(500, main)


def toplevel():
    win = Toplevel()


root.bind('<space>', lambda x: [main(), toplevel()])

root.mainloop()

When I stop pressing the 'X' button the Scale jumps to the point it should be

How can I keep the slider/scale flowing normally even when I hold down the 'X' button?
And also why does this happen?

Thanks in advance!

from Why does holding down the 'X' button in a toplevel stop execution of main window in tkinter?