What steps will reproduce the problem?

Create two annexes from the command line on two separate machines:

mkdir ~/Files.annex
cd ~/Files.annex
git init
git annex init
git annex untrust .
git annex direct

Add remote to each one pointing to the other:

git remote add [remote] [remote hostname]:Files.annex

Start assistant on both repos:

git annex assistant

Fill one repository with a few text files, and wait for them to propagate.

Edit one of the text files using vim, and save.

What is the expected output? What do you see instead?

Edited file should remain in the repo, but a significant portion of the time, the file disappeared from the repo in which it was edited (the file is present and properly synced on the other repo).

What version of git-annex are you using? On what operating system?

git-annex 4.20130323, Mac OS X on the repo where the file was edited, Arch Linux for the other paired repo.

Please provide any additional information below.

I have observed this problem setting up the repos through the webapp as well, so I don't think it is related to setting up the repos manually. I think the way vim is writing the files seems to be tickling a race condition (both command-line vim and MacVim produce the behavior). I started trying to work around it by switching to emacs to edit those files, and the files haven't disappeared from the edited repo (so far at least).