git-stash fails on OSX 10.5

Hi folks --

I'm stumped; git-stash simply won't work on my machine. On any
repository I've tried, with various permutations, I keep getting::

    $ git stash
    cp: `.../.git/index': No such file or directory
    Cannot save the current worktree state

I spent about an hour in #git this morning trying to track it down
(log: http://colabti.org/irclogger/irclogger_log/git?date=2009-04-10#l1946).
I've tried stashing with and without content added to the index; I've
also tried entirely removing .git/index and then recreating it via git
reset. No dice.

I'm entirely willing to entertain the possibility that this is my
fault, but I am fairly familiar with git (been using it for about a
year) and so if it is fault it's gotta be something pretty subtle.

I'm concerned by the fact that it doesn't work on *any* repository on
my machine, though. I think that points to a systematic problem.

I'm on OS X 10.5.6; Git is 1.6.2.2, built and installed from source,
though the same problem happened with the old 1.6.0 I had yesterday,
and also the 1.6.2.1 I installed via the OSX package.

Thanks!

Jacob