git status and diff-files don't agree on unmerged file

I've run into an issue recently where I'll be rebasing, hit a
conflict, resolve it, use "git add" (I think...) but rebase doesn't
want to continue. It seems there is a disagreement between diff-files
and status while in this state:

$ git --version
git version 1.7.0.1.242.ga1f88

$ git status
# Not currently on any branch.
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#	modified:   chrome/browser/cocoa/browser_window_controller.mm
#	modified:   chrome/browser/cocoa/tab_strip_controller.h
#	modified:   chrome/browser/cocoa/tab_strip_controller.mm
#
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#	.mailmap

$ git diff-files --ignore-submodules
:100644 100644 b6ac7eb5e74d21eb7d5806f05a2ed83d6078ced3
0000000000000000000000000000000000000000
M	chrome/browser/cocoa/tab_strip_controller.h

git add on the file in question resolves the problem, but shouldn't
said file show up as "unmerged" in the output of git status?

j.