reclassifying slash-in-path
slash-in-path: explanation in its commit message

that is, the $shocking_commit_message, not what you read here.

Actually, I should research a little deeper than I wrote there:

"git checkout frightening/slash-in-path" prints

    D     hello/world
    A     hello/world

(which is inconsistent), git status says "working directory clean", then
git checkout master fails (untracked file that would be deleted).