[BUG?] git-merge appends extra string to user's message?

When "git merge" is run with a message, it appends an extra message 
that it would add if it were run without one. For example, when I 
tried to merge an early part of a side branch.

% git merge -m "Merge early part of side branch" `git rev-parse side~2`
% git show -s 
commit 37217141e7519629353738d5e4e677a15096206f
Merge: e68e646 a1d2374
Author: しらいし ななこ [off-list ref]
Date:   Wed Dec 2 14:33:20 2009 +0900

    Merge early part of side branch

    Merge commit 'a1d2374f8f52f4e8a53171601a920b538a6cec23'

I gave my own message because I didn't want git to add the 
standard message (if I wanted to, I wouldn't have given one, 
or I would have prepared it using git-fmt-merge-msg command).

Is it possible to tell git-merge not to do this, or will it 
break compatibility and is a bad idea to change it?

I noticed that this was proposed before:

 http://thread.gmane.org/gmane.comp.version-control.git/77965/focus=80059

you were in favor of changing this behavior, and there was 
no objection from the list.

-- 
Nanako Shiraishi
http://ivory.ap.teacup.com/nanako3/