[Tkinter] Checkboxes in different frames misbehave

[jfong]

import tkinter as tk

root = tk.Tk() 
Frame1 = tk.Frame(root)
Frame2 = tk.Frame(root)

Frame1.pack()
Frame2.pack()

tk.Checkbutton(Frame1, text="checkbutton #1").pack()
tk.Checkbutton(Frame2, text="checkbutton #2").pack()

root.mainloop()

Why does it check both checkbuttons if I click only one and how can I make them independent without putting both in the same frame?

There are two independent frames and checkbuttons. You can see it simply by modifying:
Frame1 = tk.Frame(root, bg='red', padx=10)

And in my test, I didn't see both checkbuttons can be checked by a single click.