Tkinter画布内嵌滚动Frame未居顶且可向上滚动问题排查

我开发一款GUI工具时遇到了棘手问题：将可滚动Frame嵌入Canvas后，Frame并未处于Canvas顶部（期望是居顶显示），且Canvas还能向上滚动到Frame上方的空白区域（Frame背景为绿色，Canvas背景为黄色），这属于异常行为。我反复检查修改代码都没能解决，求各位提供排查思路，感谢！

代码如下： #

import tkinter.ttk as ttk
from tkinter import *
    
root = Tk()
root.title("Checklist Buddy")
root.config(padx=10, pady=5)
root.geometry("800x500")

top_frame = Frame(root, bg="black")
top_frame.grid(row=0, column=0, sticky="NSEW")

mf = Frame(root, bg="brown")
mf.grid(row=1, column=0, sticky="NEWS")

canvas = Canvas(mf, bg="yellow")
canvas.grid(row=0, column=0, sticky="NEWS")

yscrollbar = ttk.Scrollbar(mf, command=canvas.yview)
yscrollbar.grid(row=0, column=1, sticky="ns")

canvas.bind('<Configure>', lambda e: canvas.configure(scrollregion=canvas.bbox("all")))
canvas.configure(yscrollcommand=yscrollbar.set)

bpo_frame = Frame(canvas, background="green")
win = canvas.create_window((0, 0), window=bpo_frame, height=100)


def _on_mousewheel(event):
    canvas.yview_scroll(int(-1 * (event.delta / 120)), "units")


def onCanvasConfigure(event):
    canvas.itemconfigure(win, width=event.width)


canvas.bind('<Configure>', onCanvasConfigure, add="+")
canvas.bind_all("<MouseWheel>", _on_mousewheel)

root.columnconfigure("all", weight=1)
root.rowconfigure("all", weight=1)

mf.columnconfigure(0, weight=1)
# mf.rowconfigure("all", weight=1)

root.mainloop()

问题示意图： #

内容的提问来源于stack exchange，提问作者Bumblebee