NFS warnings: Directory attributes ... are of the wrong dir

Hello,

we have a Tru64 5.1A system here which mounts some large filesystems
via NFS (v3). We recently extended the capacity of the NFS server
(which now runs Linux 2.6.19) and switched the underlying filesystem
from ReiserFS to XFS. Since then we are seeing an NFS-related
warning in the logs of the Tru64 system:

Feb  5 18:56:39 cheetah vmunix: NFS3 LOOKUP: Directory attributes from hamilton are of the wrong dir.

(cheetah is the Tru64 system; hamilton the NFS server.)

This is repeated every few minutes, unregularly. It seems to depend
on the access pattern, but I couldn't figure out the details yet.
As far as I can tell, the actual operation of the system is not
affected, but of course the effects might be subtle.

Other NFS clients (which run Linux, 2.4 or 2.6) show no warnings.
The mounted filesystems in question have the following sizes:
 15GiB / 1600GiB / 4000GiB

Interestingly, "df" reports a bogus size for the 4000GiB volume:
The system's df reports (/sbin/df -k):
 Filesystem               1024-blocks        Used   Available Capacity Mounted on
 hamilton:/worka           -100794368  1246266960           0 -1235% /worka
while the GNU df (GNU fileutils 4.0) reports (/usr/local/bin/df -k):
 Filesystem           1k-blocks                  Used Available Use% Mounted on
 hamilton:/worka      18446744073608757248 1246267172         0 100% /worka
But I guess (and hope) these are simply bugs in the "df" applications.

Anyway, the first NFS warnings already appeared before the 4000GiB
volume was mounted, so these are probably unrelated problems.

I have searched this list as well as Google and Google groups,
but I could not find any mention of this particular NFS warning
message.

My question is: Has anybody ever seen such a warning?
Is it something to worry about, or can it safely be ignored?
Does Tru64 have any trouble with NFS volumes larger than 2TiB?

Best regards,
Frank