>Looking at that documentation, I can't see no bug in the implementation.

As an extra data point, Python's os.path.basename("a/b/c/") returns "".
It is defined to return "the final component of a pathname".

Python's basename/dirname pair have the same concatenative properties
as O'Caml's so this makes sense in both languages.

This is probably also more useful than the semantics of basename(1).