I accidentally changed some metadata tags for all annexed files in a directory (by omitting the filename to the git annex metadata call). How can I revert that change?

I tried a git reset --hard on the git-annex branch, but after checking out master and adding a new file the changes magically reappeared.

git-annex version: 5.20141125

To reproduce do:

git init; git annex init
echo Hi > a.txt; git annex add a.txt
git commit -m 'Initial add'
git annex metadata --set name=bla
git annex metadata --set name=blu
git checkout git-annex
git reset --hard HEAD^
git checkout master
git annex metadata a.txt # name=bla
echo Huch > b.txt; git annex add b.txt
git annex metadata a.txt # name=blu again