chown 5.0.91 bug, regarding "." and ":"

i've compiled chown on a gentoo gnu/linux system, the 
program reports its version as 5.0.91.
it seems to no longer accept a user followed by a group with a separator
as a full-stop (the colon works fine).
this means I get:
# chown root. *
chown: `root.': invalid user
# chown root.audio *
chown: `root.': invalid user

but:
# chown root *
succeeds, as does
# chown root:audio *
etc...

Note, that this is the exact opposite effect that was intended by
deprecating the ":" option. The wrong one got cancelled. Can someone
explain the reason for doing so; perhaps in the manpage? since the man
page says that both are still acceptable.

dylan.
    http://robotics.usc.edu/~dshell