Tar changes folder ownership when run under root

[Zsolt Ero]

I got locked out of my server via SSH, simply by extracting a tar file. No matter how crazy it sounds, it is reproducible.

1. login as root
2. wget https://github.com/aristocratos/btop/releases/download/v1.0.9/btop-1.0.9-linux-x86_64.tbz`
3. tar -xjvf btop-1.0.9-linux-x86_64.tbz`

At this point the /root folder has ownership of user:user (1000:1000) and the root is locked out from SSH login. I had to fix the server via KVM.

auth.log contained the following:
"Authentication refused: bad ownership or modes for directory /root"

This seems to be a bug in tar, as the above behaviour doesn't happen when logged in under any non-root user.
With non-root users the directory does not change ownership.
With root user, no matter where I extract the tar file, the directory changes ownership.

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lsb_release -rd
Description: Ubuntu 18.04.6 LTS
Release: 18.04

apt-cache policy tar
tar:
  Installed: 1.29b-2ubuntu0.2
  Candidate: 1.29b-2ubuntu0.2