I have a number of files that belong to my user account (running after become dibabel):
$ ls -alh /data/project/dibabel/www/static/dbg/i18n/ ... -rw-rw-r-- 1 yurik wikidev 11K Sep 26 15:03 en.json
Running take en.json shows en.json: You need to share a group with the file
Running chown or chgrp results in Operation not permitted
Relevant code is here