sparse file issue?, dd(1) works well but tar(1) not on different partition

Hi sparse guys (?)

I have been wondering about sparse file transportation between different
partitions on -current. For example,

   /localapps/qemu/ on local disk (UFS2)
   /nfshome/user/ on NFS (UFS2)

   /localapps/qemu/disk0image  20GB qemu diskimage sparsed file

then, follow operation works well.

   # cd /localapps/qemu/
   # tar cpf - disk0image | tar xpf - -C /nfshome/user/
   # cd /nfshome/user/
   # dd if=disk0image of=disk0image-sparse conv=sparse

But

   # cd /localapps/qemu/
   # tar cpf - disk0image | tar xpf - -S -C /nfshome/user/

gets follow error message.

   # tar cpf - disk0image | tar xpf - -S -C /nfshome/user/
   disk0image: Write request too large
   tar: Error exit delayed from previous errors.
   #

tar(1) cannot do sparse output between different partations?
Have I missed something important point?  If you have any ideas,
teach me.

Thanks :)

-- 
   Daichi GOTO, http://people.freebsd.org/~daichi