> Perhaps this is the same problem as pr 8249, which has been fixed quite
> a while ago already. I don't know if the changes made it to the release
> branch though.

It did -- snipping from CHANGES-1.4.2:

sys/nfs/nfs_socket.c                            1.52-1.53

  Fix overzealous DIAGNOSTIC check in nfs_disconnect() and
  don't try to copy a possibly freed mbuf.  Fixes PR#8249, PR#8288
  and PR#8766.

Regards,

- H=E5vard