git fetch inside a bare repo does nothing

kblin on IRC wanted to know how to update a bare repo with fetching.
He wants to have a bare repo of samba as a mirror and clone from this
mirror to avoid network traffic and to have several git repos which
could all have a different branch checked out. For a better description
see [1].

I suggested to use "git fetch --bare" inside the bare repo, but this
doesn't work. So what I'm asking now if this is intenional behaviour or
a bug, so please could someone  shed some light on it?  Or how is the
prefered method to update a bare repo *without* pushing to it?

-Peter

[1]: http://wiki.samba.org/index.php/Using_Git_for_Samba_Development

IRC log (unneccessary comments removed):

11:30 < kblin> how do I update a branch I cloned with --bare?
11:31 < madduck> GIT_DIR=/path/to/dir git pull >
11:31 < madduck> ?
11:31 < madduck> without the >
11:32 < kblin> and for remote repositories, I'd use a URL?
11:37 < madduck> uh, you can't reallly "update" remote repositories in that sense
11:37 < madduck> what are you trying to do?
11:37 < madduck> let's have more info!
11:51 < kblin> madduck: I'm trying to follow http://wiki.samba.org/index.php/Using_Git_for_Samba_Development
11:52 < kblin> madduck: basically, I want to have a --bare repository that mirrors the remote repository
               and have a couple of working repositories for the different branches
11:57 < siprbaum> kblin: I think "git --bare fetch" inside your bare repo will solve your problem
[...]
12:01 < kblin> siprbaum: git --bare fetch doesn't seem to fetch anything new either
12:01 < siprbaum> perhaps there isn't anything new to fetch?
12:02 < siprbaum> but i'm just guessing here and reading the manpage (git) suggested that git --bare fetch _could_ work
12:02 < kblin> siprbaum: that'd surpise me. I've got a clone without the --bare, and that has a new commit
[...]
12:14 < siprbaum> kblin: and you are right. i just tried to fetch inside a bare repo and it doesn't work