Trying to copy files and preserve ownership
Are you copying to a mounted volume that is on another system? If so, it may be confusing the uid and gid's.

Or are you copying to a NAS which might have an override setting for the ownership of the connected user. For example FreeNAS has options for NFS mounts to Mapall User and Mapall Group, and for AFP mounts to set default file and directory permissions

you can check for uid with something like
    dscl . -read /Users/ UniqueID
and check for group id with
    cat /etc/groups
or
    dscacheutil -q group

Could you try tar'ing up a few files, copying them to the new volume and then untar'ing them and then check the file permissions?