Dietmar Schindler added the comment:
Regarding Issue8243: This issue is about writing the lower-right character of a
window via *addch()* or *addstr()*. But for curses.textpad.Textbox(win).edit()
the use of *addch()* or *addstr()* is not unavoidable; it could well use
*insch()* or *insstr
New submission from Dietmar Schindler:
curses.textpad.Textbox(win).edit() does not allow to enter a character (or
change one, if already there) at the very last position in a window (the lower
right hand corner), though it allows to position the cursor there. This applies
to the whole screen
