NFS clients report different file sizes on same file

We have several RedHat Enterprise 3 clients mounting a filesystem from
an Adaptec Snap Server using NFS. We're seeing an occasional issue
where 2 or 3 of the clients report an incorrect file size for random
files. The date and time on the file is identical. All Linux clients
are running Enterprise 3 update 6 (kernel 2.4.21-37.EL).

eg

eoin@edc-moy(eoin)$ ls -l
/usr/cadtools/bin/xadice5.dir/scripts/lintel/gain_phase.o
-r--r--r-- 1 adicedst users 15886 Jun 15 02:46
/usr/cadtools/bin/xadice5.dir/scripts/lintel/gain_phase.o

eoin@edc-redhat(eoin)$ ls -l
/usr/cadtools/bin/xadice5.dir/scripts/lintel/gain_phase.o
-r--r--r-- 1 adicedst users 79984 Jun 15 02:46
/usr/cadtools/bin/xadice5.dir/scripts/lintel/gain_phase.o

All the other files in the dir are correct. The server shows the file
as 79984 as do our Solaris NFS clients.

Could anyone suggest what may be happening ?

Many thanks,
Eoin