bug#7283: 23.2; whitespace-mode breaks scrolling with partial line visible at top of buffer

[Eli Zaretskii]

> From: Anders Kaseorg <andersk@MIT.EDU>
> Date: Tue, 26 Oct 2010 15:43:48 -0400
> Cc: 
> 
> When whitespace-mode is enabled and the buffer is scrolled such that
> only part of a long line is visible at the top of the buffer, it becomes
> impossible to scroll the window down using the down arrow.
> 
> This can be reproduced from ‘emacs -Q’ with
>   C-u 99 <return>
>   M-<
>   C-u 99 a
>   C-u 0 C-l
>   M-x whitespace-mode
> followed by pushing <down> until the window scrolls (it won’t!).

I can reproduce this in Emacs 23.2, but not in Emacs 24.0.50.