Upload files from <input type=file> with the download request

I am missing the files selected in an `<input type="file">` element. Sending the form regularly, send the files and i can access them in my python flask server via `request.files.getlist('file')`. This one is empty now with jQuery.fileDownload. I suspect that they are not sent with the request.

Is there a solution i am missing or is it simply not implemented?