"chgrp: operation not permitted" during cvs update

[Thomas Klausner <wiz%NetBSD.org@localhost>]

Since my last update (from 5.99.22/20091115 to 20091124), cvs update
now reports:
chgrp: ./tools/obj: Operation not permitted
chgrp: ./obj: Operation not permitted
That's correct, because I'm updating as a user that's not the owner of
those dirs, but it never reported that before. Any idea what changed?

# ls -l /usr/src/obj
total 4
drwxrwxr-x   2 root  builder   512 Oct  4 12:45 .
drwxrwxr-x  29 wiz   builder  1024 Nov 25 19:43 ..

 Thomas