Terry J. Reedy added the comment:
You only need to run .update_idletasks(), as there are no pending events to
process.
This is not a tkinter issue. It is a known fact that there are undocumented
annoying differences in tk behavior on different systems and even different
versions thereof.
New submission from Novel :
Code to reproduce the problem:
```
import tkinter as tk
from tkinter.messagebox import showinfo
root = tk.Tk()
entry = tk.Entry(root)
entry.pack()
# root.update() # remove comment to fix the problem
showinfo('alert', 'this parrot is dead!')
root.mainloop()
```
