When using remount on nfs exports, several strange things happen:

#mount
/some/nfs/export on /nfs type nfs
(ro,soft,intr,bg,rsize=8192,wsize=8192,addr=192.168.100.100)

#mount -o remount,rsize=2048,wsize=2048 /nfs
#mount
/some/nfs/export on /nfs type nfs
(ro,soft,intr,bg,rsize=8192,wsize=8192,rsize=2048,wsize=2048,addr=192.168.100.100)

also, if you remount, existing options may be removed:
#mount
/some/nfs/export on /nfs type nfs
(ro,soft,intr,bg,rsize=8192,wsize=8192,addr=192.168.100.100)

#mount -o remount,timeo=20 /nfs
#mount
/some/nfs/export on /nfs type nfs
(ro,soft,intr,bg,rsize=8192,wsize=8192,timeo=20,addr=192.168.100.100)
#mount -o remount,actimeo=60 /nfs
#mount
/some/nfs/export on /nfs type nfs
(ro,soft,intr,bg,rsize=8192,wsize=8192,actimeo=60,addr=192.168.100.100)

I would expect that timeo would not be replaced by actimeo in the second
mount.  Both mount(8) and nfs(5) are silent on what the defined behavior is
supposed to be, but mount does not do this replacement on local
filesystems.  I have also seen mount append multiple "addr=" entries when
doing a remount of an NFS export.