chown -vs- `.' in username

[Tom Tromey]

I tried to create a user "m.ring" on sourceware.
Then I did "chown -R m.ring /home/m.ring"
chown complains about the username, perhaps because it is
misinterpreting it as "user m, group ring" (?).

    [root@sourceware ~m.ring]# chown -R m.ring .
    chown: m.ring: invalid user

Tom