rebase not honoring core.worktree pointing elsewhere

[Paul Drews <paul.drews@intel.com>]

Hello,

I'm observing an unexpected error from "git rebase" run from the directory
containing the ".git" directory:

$ git --version

git version 1.7.3.GIT
(includes up to commit ca2090 from git repository at
http://www.kernel.org/pub/scm/git/git.git)

$ mkdir wherefilesare
$ mkdir wheregitis
$ cd wherefilesare
$ echo "Here is a line from the original" > myfile.txt
$ cd ../wheregitis
$ git init
$ git config core.worktree /absolute/path/to/wherefilesare/
$ git add .
$ git commit
$ git branch mybranch
$ git checkout mybranch
$ vim ../wherefilesare/myfile.txt 
$ git add .
$ git commit
$ git checkout master
$ vim ../wherefilesare/myfile.txt 
$ git add .
$ git commit
$ git checkout mybranch
$ git rebase master

fatal: /usr/libexec/git-core/git-rebase cannot be used without a working tree.

Since I'm in the directory containing ".git" at this point, the ".git" directory
and the worktree can be unambiguously found.  Other commands besides "git
rebase" work.  I would expect "git rebase" to work as well.  Is this a bug or an
unreasonable expectation on my part?