Reset sometimes updates mtime

[Dennis Kaarsemaker <dennis@kaarsemaker.net>]

I'm seeing some behaviour with git reset that I find odd. Basically if I
do

git fetch && \
git reset --hard simple-tag-that-points-to-the-current-commit

sometimes the reset will update the mtime of all files and directories
in the repo and sometimes it will leave them alone. Changing it to

git fetch && \
git status && \
git reset --hard simple-tag-that-points-to-the-current-commit

Cause the mtime update to reliably not happen.

Bad thing is that I am relying on the mtime updates not to happen if the
files don't actually change. Is this an assumption I can safely make? If
it is, then I'll debug further (e.g. I don't even know yet if the file
gets rewritten or just touched, why the index gets updated as well
etc.).

-- 
Dennis Kaarsemaker
http://www.kaarsemaker.net