git being git

gittest.sh

/tmp$ mkdir gittest
/tmp$ cd gittest
/tmp/gittest$ git init
/tmp/gittest$ echo test > test
/tmp/gittest$ git add test
/tmp/gittest$ git commit -m test
/tmp/gittest$ git diff-index --quiet HEAD
/tmp/gittest$ echo $?
0
/tmp/gittest$ echo "another test" >> test
/tmp/gittest$ git diff-index --quiet HEAD
/tmp/gittest$ echo $?
1
/tmp/gittest$ echo test > test
/tmp/gittest$ git diff-index --quiet HEAD
/tmp/gittest$ echo $?
1 # what?
/tmp/gittest$ git status
/tmp/gittest$ git diff-index --quiet HEAD
/tmp/gittest$ echo $?
0 # expected...