12.04 - running git status resets permissions on index file

Trying to sort out if this is a git bug or something with Ubuntu. Basically about half the time an interaction with the git index file results in the permissions on that file being changed to the point that I can't do the same command again. Like so:

$ ll .git
total 156K
...
drwxrwxrwx   2 dev dev 4.0K Jul 23 09:30 hooks
-rwxrwxrwx   1 dev dev  17K Aug  8 13:12 index
drwxrwxrwx   2 dev dev 4.0K Jul 19 09:31 info
...


$ gs
# On branch build-0.3
# Your branch is ahead of 'staging/build-0.3' by 5 commits.
#   (use "git push" to publish your local commits)
#
# Untracked files:
#   (use "git add ..." to include in what will be committed)
#
#   scripts/loadDb.coffee

nothing added to commit but untracked files present (use "git add" to track)

$ ll .git
total 156K
...
drwxrwxrwx   2 dev dev 4.0K Jul 23 09:30 hooks
-rw-rw-r--   1 dev dev  17K Aug  8 13:16 index   # <------ this line  
drwxrwxrwx   2 dev dev 4.0K Jul 19 09:31 info
...


$ git --version
git version 1.8.3.4

$ lsb_release -a
Distributor ID: Ubuntu
Description:    Ubuntu 12.04.2 LTS
Release:    12.04
Codename:   precise

I've submitted a bug report to the git mailing list, but that list is so user-unfriendly that I can't tell if it's actually been submitted. It's also possible that I've done something wrong in Ubuntu and that's what is causing it.

This has only been happening since I switched over to 12.04 64b but I can't say with certainty that that is exactly when it happened.