comment-region rather aggressive when uncommenting

[Roland Winkler]

In GNU Emacs 21.2.1 (i386-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2002-04-09 on tfkp12
configured using `configure  --prefix=/nfs/common --libexecdir=/nfs/common/lib 
--bindir=/nfs/common/lib/emacs/21.2/bin/i686-Linux 
--mandir=/nfs/common/share/man --infodir=/nfs/common/share/info --with-gcc 
--with-pop --with-x --with-x-toolkit=athena i386-pc-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_DE@euro
  locale-coding-system: iso-latin-9
  default-enable-multibyte-characters: nil

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

Suppose I have in shell-script mode the following lines:

# foo
# # ===============================================
# # ===
# bar

When I uncomment these lines with C-u M-x comment-region I get

foo
# # ===
bar

i.e., the second line is deleted completely. Isn't that a little too
aggressive? I am most surprised that only the second line is
deleted, but not the third line.
(I like the "# =====" for structuring my shell scripts.) 

Same with GNU Emacs 21.2.50.2.

Roland