Today, trying upload to jessie-backports from a Jessie jail, I got this message from dput-ng:

 $ dput netdiscover_0.3beta7~pre-2~bpo8+1_amd64.changes
Uploading netdiscover using ftp to ftp-master (host: ftp.upload.debian.org; directory: /pub/UploadQueue/)
running allowed-distribution: check whether a local profile permits uploads to the target distribution
`jessie-backports' not in the codename group

To solve this problem, you can edit the /usr/share/dput-ng/codenames/debian.json file and add jessie-backports here:

 "backport": [
 "stable-backports",
 "oldstable-backports",
 "jessie-backports",
 "wheezy-backports",
 "squeeze-backports"
 ],

I hope this help someone.