NFS permissions skewed with linux 2.6 client

[Wouter Hanegraaff <wouter@openoffice.nl>]

Hi,

I'm experiencing weird problems with file permissions on nfs-mounted
directories: even though I am in the group users, I can't write to
files in the directory test which is supposed to be writable by users.
See the following transcript:

 bash-2.05a$ whoami
 wouter
 bash-2.05a$ groups wouter
 wouter : wouter adm dialout floppy cdrom users openoffice src tape mysql telnetd video staff audio
 bash-2.05a$ pwd
 /home/algemeen
 bash-2.05a$ ls -la test
 total 8
 drwxrwsr-x    2 valentyn users        4096 Aug 25 12:03 .
 drwxrwsr-x   25 root     openoffi     4096 Aug 25 12:03 ..
 bash-2.05a$ mount|grep home
 server:/home on /home type nfs (rw,rsize=4096,wsize=4096,addr=192.168.112.11)
 bash-2.05a$ touch test/hallo
 touch: creating `test/hallo': Permission denied

The NFS client uses a 2.6 kernel, the server uses a 2.4 kernel.  If the
nfs client is booted with a 2.4 kernel, there's no problem at all. On
the server there's also no problem at all, an on local filesystem the
group permissions also work as usual.

What could be the problem here? Has anyone seen this before?
Version info: 
Client nfs-common: Version: 1:1.0.6-0.bunk
Server nfs-kernel-server: Version: 1:1.0-2woody1

Best regards,

Wouter