$uid = 99;
# $> = 0
$gid = "99 2 99";
# $) = "0 1 0"

##</code><code>##

$> = $uid;
$) = $gid;

# Current values are now:
# $> = 99
# $) = "0 1 0"

##</code><code>##

$) = $gid;
$> = $uid;

# Current values are now:
# $> = 99
# $) = "99 2 99"
# Which is the desired outcome

##</code><code>##

($>, $)) = ($uid, $gid;)

# Current values are now:
# $> = 99
# $) = "0 99 2"
# The other groups section has been successfully changed,
# but the actual effective gid has not.