Why Chown on a file/directory to the root user does not respect NFSv4 no_root_squash?

Issue

• When mounting a NFSv4 mount point using the option 'no_root_squash', user 'root' can create files on that filesystem, and the ownership is correct:

[root@client ~]# touch /mnt/some/yyy
[root@client ~]# ls -l /mnt/some/yyy
-rw-r--r--. 1 root root 0 Oct 15 18:03 /mnt/some/yyy

But when using 'chown' to 'root:root', the ownership is changed to 'nobody:nobody':

[root@client ~]# chown root:root /mnt/some/yyy
[root@client ~]# ls -l /mnt/some/yyy
-rw-r--r--. 1 nobody nobody 0 Oct 15 18:03 /mnt/some/yyy

Client and server both have a FQDN, the domain is explicit in /etc/idmapd.conf and the file is the same.

• Why chown fails to change ownership of root user and sets the ownership as nobody on NFS client?
• Why chown does not work for root user even when share is exported with no_root_squash?