strange behaviour of NFS

[Tony_Melia Dell com]

I am using redhat 6.0 to mount a SCO Openserver 5.0.5 NFS share.  I for had
permission problems, but I managed to get them sorted and mount the share.
I mount it under /shared.  If I use 'dd if=/dev/zero of=/shared/test bs=1k
count =1000' to create a 1M test file, it is stored on the local filesystem
instead of going over the network to the /shared directory.  If I do an ls
after doing the dd command, I cannot see the test file, I can only see it
after I unmount /shared.  I have had no problem mount linux <-> linux
shares.

It is as if files are readable over the NFS link, but new files are created
locally...the same way as the overlay filesystem works.  I am mounting it
with 'defaults,rw' as the only mount option.