lockd: cannot unmonitor

[VSJ <debian@terabytemusic.cjb.net>]

Hi,

I've an NFS client running an up-to-date Debian sid, kernel 2.4.27 (not
vanilla, but supplied by Debian).

If someone tries to shut down this machine, the machine doesn't power-off!

These are the last fews messages printed to the console:

1 lockd_down: lockd failed to exit, clearing pid
2 flushing ide devices: hda hdc
3 Power down.
4 lockd: cannot unmonitor 192.168.1.1
5 portmap: server localhost not responding, timed out

I've added line numbers, so I can comment on each line:
at 3, Power down, the harddisk is being turned off (I can hear that), but
the rest of the computer stays on. After a few seconds, message 4 appears.
Than after a (few) minutes, message 5 appears. This message keeps repeating
itself after a certain interval. 
This all happens after the local filesystem is unmounted, so there are no
useful logfile entries.

The host 192.168.1.1 is the NFS server. It is running Debian woody with
kernel 2.4.27.
Log files (messages, user.log, syslog) from the server show the following:
Oct  8 17:17:21 P1 rpc.mountd: authenticated unmount request from P4:682
for /var/share (/var/share)
Oct  8 17:17:21 P1 rpc.mountd: authenticated unmount request from P4:684
for /home (/home)


(the server's name is P1, the client's name is P4)

My own computer is running an up-to-date Debian sid, too, but doesn't suffer
from this shut-down problem. The only difference is that I'm running kernel
2.6.7, not 2.4.27.

Does anyone know how I can fix this problem?

Thanks in advance,
Stanley.
PS: if you need more info, let me know.