"Failed to preserve ownership" exit(1) bug in mv?

[Jim Minter]

Hello,

A behaviour that surprised me with mv, moving files to an NFS-mounted 
filesystem with all_squash set (in a Vagrant box running Fedora 25, 
coreutils 8.25).

(/vagrant is NFS-mounted as described in the example below).

==== 8< ====
[vagrant@default ~]$ sudo -i
[root@default ~]# ln -s thing symlink
[root@default /]# mv symlink /vagrant
mv: failed to preserve ownership for /vagrant/symlink: Operation not 
permitted
[root@default /]# echo $?
1
[root@default /]# ls . /vagrant
.:
symlink

/vagrant:
symlink
==== 8< ====

The surprise to me is that mv exits early in this case (after copying 
the symlink across volumes, before removing the source symlink).

Doing the same operation as root but with a regular file, I get the same 
warning message, but the move completes as expected, and mv returns exit 
status 0.  I had expected the same behaviour when moving a symlink.

(As non-root, mv works as expected both for a file and for a symlink - 
object moved, chown syscall fails, no warning message).

The knock-on effect I've seen which is particularly problematic, is that 
this issue causes mv to fail when moving an entire directory tree as 
root to an NFS-mounted filesystem, if that directory tree contains a 
symlink anywhere within it.  Can the exit(1) in this case be considered 
a bug?

Best regards,

Jim