M-x sort-lines and M-x sort-fields always set the buffer modified
status ("-" -> "*" in column 5 of the status line), even if the region
was sorted and the command did not modify anything.
An unmodified buffer should stay unmodified if nothing was changed.
Reproduction:
C-x C-f a <return> a <return> b <return> c <return> C-x C-s <C-home> 
M-x s o r t - l <tab> <return>
Status line should start with --\---, it starts with --\**-


In GNU Emacs 23.1.1 (i386-mingw-nt5.1.2600)
 of 2009-07-30 on SOFT-MJASON
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (4.4)'

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  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: DEU
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8
  default-enable-multibyte-characters: t

Major mode: Fundamental

Minor modes in effect:
  show-paren-mode: t
  display-time-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t

Recent input:
C-s C-s C-s C-a <up> <up> <S-down> <S-down> <S-down> 
<S-down> <S-down> <S-down> <S-down> <S-down> <S-down> 
<S-down> <S-down> <S-down> <S-down> <S-down> <S-down> 
<S-down> <S-down> <S-down> <S-down> <S-down> <S-down> 
<S-down> <S-down> <S-down> <S-down> <S-down> <S-down> 
<S-down> <S-down> <S-down> <S-down> <S-down> <S-down> 
<S-down> <S-down> <S-down> <S-down> <S-down> <S-up> 
<S-up> <S-up> <S-up> <S-up> <S-up> <S-up> <S-up> <S-up> 
<S-up> <S-up> <S-up> <S-up> <S-up> <S-up> <S-up> <S-up> 
<S-up> <S-up> <S-up> <S-up> <S-up> <S-down> <S-down> 
<S-down> <S-down> <S-down> <S-down> <S-down> <S-down> 
<S-down> <S-down> <S-delete> <S-up> <S-up> <S-up> <S-down> 
<S-delete> <delete> C-s C-s C-a <f11> C-s C-s C-s C-s 
C-s C-s C-s C-s C-s C-s C-s C-s C-s C-s C-a <down> 
<down> <down> <down> <down> <down> <down> <down> <down> 
<down> <down> <down> <down> <down> <down> <down> <down> 
<down> <down> <down> <down> <down> <down> <down> <down> 
<down> <down> <down> <down> <down> <down> <down> <down> 
<down> <down> <down> <down> <down> <down> <down> <up> 
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up> 
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up> 
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up> 
<up> <up> <up> <up> <up> <up> <C-right> M-. <return> 
<lwindow> <help-echo> <help-echo> <help-echo> <lwindow> 
<f1> i <f2> <M-backspace> e t <tab> p r <tab> <return> 
<C-home> C-s s o r t C-s C-s C-a <C-home> <lwindow> 
<f3> <return> C-s s o r t C-s C-s C-a <C-home> <down> 
<down> <down> <down> 2 C-s C-s <down> <up> <return> 
C-s m o d i f C-s C-s C-s C-s C-a <lwindow> <f9> a 
<tab> <return> C-g <f2> a <return> a <return> b <return> 
c <return> <f3> <return> y e s <return> <f2> c : \ 
a <return> a <return> b <return> c <return> <f11> <C-S-home> 
<C-end> M-x s o r t - l <tab> <return> C-_ <lwindow> 
M-x r e p o <tab> r <tab> <return>

Recent messages:
Mark saved where search started
Mark set
Mark saved where search started [2 times]
Quit
(New file) [2 times]
Saving file c:/a...
Wrote c:/a
Mark set [3 times]
Undo!
Making completion list...

-- 
Mit freundlichen Grüßen
Roland Meier
     \|||/ 
     (o o) 
==ooO==U==Ooo== 
mailto:rm369@arcor.de