I really don't know if I must report this as a bug, as a feature request, or even as a documentation tip.
So I let the maintainers choose what it's all about.

The fact is that I used to install Filefield paths and when I started using Storage API, even if the upload worked fine (directly to an S3 bucket), the system message dropped always an error: "mynewuploadedfile was not copied because it would overwrite itself."

I figured out that uninstalling Filefield Paths remove this error message, however I still benefit of a transliteration filename.
Though I cannot manage folders through tokens on the remote storage, because I use several buckets that is just fine for me.