bug#3805: 23.1.50; Strange cursor movement in truncation mode

[Teemu Likonen]

On 2009-07-10 11:23 (+0200), Kees Bakker wrote:

> Here is an example file to reproduce the bug.

> Resize your screen to 50 characters wide, and do a toggle-truncate-lines.
> Emacs23-gtk will show arrows on the right (and left) for the part of the
> lines that is not visible.
>
> Move the cursor to the end of the first line. Then move down, up and
> down. And again up, down, up, down. You'll see that the cursor does not
> go the same position in the second each time.
>
> Second experiment.
> Move cursor further down to the line after these three long lines, and
> then move up again. And repeat that a few times, and you'll see that the
> cursor is not coming back to the same position each time.

This bug affects only when line-move-visual=t. But yes, I can reproduce
it with 23.0.96. This is related bug:

    "next-line and previous-line don't keep the column in text-scale-mode"
    http://emacsbugs.donarmstrong.com/cgi-bin/bugreport.cgi?bug=3668

I can see now that line-move-visual=t is the cause there too.