after change function not invoked on all changes in *Messages*

[Milan Zamazal]

In GNU Emacs 21.3.2 (i386-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2003-06-03 on blackbird, modified by Debian

When I try to install a local after change function on the *Messages*
buffer, it's not invoked on insertions to that buffer via the `message'
function and some other functions.  When I edit the buffer manually, the
after change function gets invoked as expected.  On deletions, the after
change function seems to be always invoked.

Try the following:

- Eval the following code:

   (defvar foo nil)
   (defun my-after-change (&rest args)
     (setq foo (cons args foo)))

- Switch to the *Messages* buffer.

- Apply

   `M-: (add-hook 'after-change-functions 'my-after-change nil t) RET'

- Apply

   `M-: (message "hello") RET'

- There's nothing about the `hello' insertion in the variable `foo'.

- Now try to type or yank some text in *Messages*.

- `foo' should contain information about the changes.

I couldn't find anything in documentation explaining this behavior, so I
think it's a bug.