Q: where to find a hint why DHCP isn't registering a certain host with DNS

My server runs Debian GNU/Linux 3.0 (woody). I've set up DHCP and DNS on
that machine:

/etc/dhcp3/dhcpd.conf:
ddns-update-style interim;
ignore client-updates;

option domain-name "<our domain name>"
option domain-name-servers <our dns>;

default-lease-time 604800;
max-lease-time 2419200;

authoritative;

then follow the subnet, setting subnet-mask and router, a key and three
zones used for ddns.

My setup worked for all windows workstations that get their settings via
dhcp. dhcp3 registers them with the dns so they can be accessed by their
names. It even worked with a knoppix CD i booted recently which got it's
network settings via dhcp. After booting, it was accessible by using the
host name (knoppix). I now installed another Debian server. It got it's
settings from dhcp, alright. But dhcp didn't register it with the dns. And
the lease in /var/lib/dhcp3/dhcpd.leases looks different than those for
computers that were registered with dns: the uid, set ddns-fwd-name, set
ddns-txt, set ddns-rev-name and client-hostname directives are missing.

Is there any log file (apart from syslog and daemon.log - they don't contain
any errors) that I might check to find out what's going wrong? Can it be a
specific client setting (the debian defaults, by the way), that keep the
server from updating dns? I'm desperate.

By the way - is there a command (like ipconfig /renew on windows) that tells
dhclient to refresh it's lease? You see I'm a bit of a newbie, please help.

Regards,
Thomas