Yes, via NOOBS install. Only Raspbian installed - Sorry, should have mentioned that!
Found the issue. '82' is the group id of netdev when NOOBS runs, so when bsdtar sees 'netdev', it remaps it. However, within raspbian, the group id is 108.
Currently checking if creating the archive with '--numeric-owner' fixes the problem, or if it has to be specified while extracting (which would require a change to NOOBS, which we don't want). If this works, I'll re-archive root.tar.xz files for the latest release.
Thanks for helping get to the bottom of this.