NFSv4 : question on the resolution of unknown users and groups

Hi,

I am in the following situation : a file belonging to the user whose (uid, gid) is (15678,15678) is to be exported via NFS through a client and / or a server than knows nothing about this user (there is no entry in /etc/passwd, in the yellow pages or whatever is used to maintain users's maps).

When using NFSv3, I see this on the client:

   # ls -ld unknown/
   drwxr-xr-x 2 15678 15678 4096 Mar 28 11:15 unknown/

When using NFSv4 (the rpc.idmapd is running on both client and server and is configured homogeneously) I see this:

   # ls -ld unknown/
   drwxr-xr-x 2 nobody nobody 4096 Mar 28 11:15 unknown/

With wireshark I can see that the server itself replies the string "nobody" as OWNER and OWNER_GROUP. I guess the libnfslibmap (used inside the rpc.idmapd) is not resolving (15678, 15678) and returns an error, making the nfsd returning nobody. The nfs-utils-lib that I use is 1.1.5-1 (it's a F13 machine). Is what I saw a regular behaviour ? How shoud I configure the client and/or the server to have the same display in NFSv4 and NFSv3 when querying attributes on objects belonging to an unknown user ?

Regards

Philippe