Hi,
Does it help if you run 'exportfs -f'? (or wait about 15 minutes)
You can check the content of the various caches that nfsd uses in:
/proc/net/rpc
I've also recently discovered that /proc/net/rpc/auth.unix.ip/content contains the cache used by nfsd. You can flush that cache with the above command (or by writing the current time in seconds-since-epoch into the flush file).
Regards,
Rik