I am seeing this same 400 error when using `python setup.py sdist upload`, but through some trials I discovered it seems to only fail on packages that haven't already been successfully uploaded with `devpi upload` at least once prior.  I'm thinking there is some metadata or file structure in the index that gets created when going through `devpi upload` that doesn't get created with the plain setup.py approach?  

Is there a way to 'register' a package initially to an index to prime the index without using `devpi upload` so that subsequent plain setup.py works? 

Thanks