Bug? ignored files overwritten by checkout

git init git commit --allow-empty -m "init" git checkout -b test echo foo > foo git add foo git commit -am 'add foo' git checkout master echo 'Important data' > foo #[1] echo foo > .gitignore git checkout test

If I tried a `git checkout test` after [1], I would get the error message 
    error: The following untracked working tree files would be overwritten by checkout: foo
But after adding foo to .gitignore, I am able to checkout to branch test
without warning. Of course this overwrites foo to the version in test.

I tested this in version 1.8.3.4 and 1.7.10.4.