git tag bug

bug.sh

#!/bin/sh -e

mkdir gitbug && cd gitbug
git init
touch README.md
git add README.md
git commit -m "initial commit"
echo "this is the example from 'git help tag':"
GIT_COMMITTER_DATE="2006-10-02 10:31" git tag -s -m "mytag1" v1.0.1
echo "it has the correct date:"
git show v1.0.1
echo "it works without signing:"
GIT_COMMITTER_DATE="2006-10-02 10:31" git tag -m "mytag2" v1.0.2
git show v1.0.2
echo "but it does not work if you specify the message via editor:"
GIT_COMMITTER_DATE="2006-10-02 10:31" git tag -a v1.0.3
git show v1.0.3