Display problem with unusual tab width

[Ueli Schl,bd(Bpfer]

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In GNU Emacs 21.1.1 (i586-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2001-11-12 on linux
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: POSIX
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: de_CH.ISO-8859-1
  locale-coding-system: iso-latin-1
  default-enable-multibyte-characters: t

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

The following actions reproduce the bug in my emacs:

- Loading the included test file (below, close enough to minimal ;-)
- Enable truncating of long lines
- Set the tab width to 32
- Go to the end of the line
- Make the emacs window wider (mine is 86x42 by default -- I think I
  don't have any emacs-related X resources loaded).  120x4 is a size
  that I've verified.
- Use the backspace key to erase a few characters

Deleting characters backwards from the end of the line supresses the
display of several characters near the end of the line.  They can be
displayed again by hitting C-l.

Thanks for the great work anyway!

- Ueli Schl=8e4pfer

---8< Testfile below
Xxxxxxx Xxxxxx  999 / 999 99 99 xx. Xxxxxxxxxx 99       Xxxxxxxx        XX-9999 
        99. Xxxx 9999   Xxxxx xxxx xx XXX
---8< Testfile above

Oh, in case this gets word wrapped: This is basically a line of
tab-separated fields of an adress list, all on one line.

Recent input:
C-x C-f W o <tab> A d r e <tab> - <tab> T e <tab> <return> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <menu-bar> <options> <truncate-lines> M-x 
e d <backspace> <backspace> s e t - v a r i a b l e 
<return> t a b - w i d t h <return> 3 2 <return> C-e 
<backspace> <backspace> C-l C-x u C-x u <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <menu-bar> <help-menu> <report-emacs-b
ug>

Recent messages:
(emacs -q -no-site-file)
Loading disp-table...done
Loading tool-bar...done
Loading image...done
Loading tooltip...done
For information about the GNU Project and its goals, type C-h C-p.
Long Line Truncation enabled
Undo! [2 times]
Loading emacsbug...done