Unlock I/O exception on NFS4

Hello,
bzr stat on a NFS4 share works but yields an exception in the final.
As far as I can understant it, it's related to file (un)locking.

- NFS4 server is running CentOS 5.1 x86_64
- NFS4 client is running CentOS 5.1 x86. The share is hard mounted.

If anyone has a clue on what I should look for, I can try to look into NFS traffic or debug messages.

-- bzr output$ bzr stat
modified:
  bin/iseg
bzr: ERROR: [Errno 5] Input/output error
/usr/lib/python2.4/site-packages/bzrlib/lockable_files.py:110: UserWarning: file group LockableFiles(<bzrlib.transport.local.LocalTransport url=file:///home/ricardo/NHQxx2x/.bzr/repository/>) was not explicitly unlocked
  warn("file group %r was not explicitly unlocked" % self)
/usr/lib/python2.4/site-packages/bzrlib/lockable_files.py:110: UserWarning: file group LockableFiles(<bzrlib.transport.local.LocalTransport url=file:///home/ricardo/NHQxx2x/.bzr/branch/>) was not explicitly unlocked
  warn("file group %r was not explicitly unlocked" % self)
/usr/lib/python2.4/site-packages/bzrlib/lockable_files.py:110: UserWarning: file group LockableFiles(<bzrlib.transport.local.LocalTransport url=file:///home/ricardo/NHQxx2x/.bzr/checkout/>) was not explicitly unlocked
  warn("file group %r was not explicitly unlocked" % self)
/usr/lib/python2.4/site-packages/bzrlib/lock.py:79: UserWarning: lock on <closed file u'/home/ricardo/NHQxx2x/.bzr/checkout/dirstate', mode 'rb+' at 0xb792b5c0> not released
  warn("lock on %r not released" % self.f)
Exception exceptions.NotImplementedError: <exceptions.NotImplementedError instance at 0xb79e88cc> in <bound method _fcntl_TemporaryWriteLock.__del__ of <bzrlib.lock._fcntl_TemporaryWriteLock object at 0xb7928d8c>> ignored
/usr/lib/python2.4/site-packages/bzrlib/lock.py:79: UserWarning: lock on <open file u'/home/ricardo/NHQxx2x/.bzr/checkout/dirstate', mode 'rb' at 0xb7916e78> not released
  warn("lock on %r not released" % self.f)

-- bzr.log
0.079 encoding stdout as sys.stdout encoding 'UTF-8'
0.081 bzr arguments: [u'stat']
0.081 looking for plugins in /home/ricardo/.bazaar/plugins
0.081 looking for plugins in /usr/lib/python2.4/site-packages/bzrlib/plugins
0.082 Plugin name __init__ already loaded
0.082 Plugin name __init__ already loaded
0.131 encoding stdout as sys.stdout encoding 'UTF-8'
0.221 opening working tree '/home/ricardo/NHQxx2x'
0.234 check paths: None
0.270 Traceback (most recent call last):
  File "/usr/lib/python2.4/site-packages/bzrlib/commands.py", line 834, in run_bzr_catch_errors
    return run_bzr(argv)
  File "/usr/lib/python2.4/site-packages/bzrlib/commands.py", line 790, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.4/site-packages/bzrlib/commands.py", line 492, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.4/site-packages/bzrlib/commands.py", line 800, in ignore_pipe
    result = func(*args, **kwargs)
  File "/usr/lib/python2.4/site-packages/bzrlib/builtins.py", line 189, in run
    to_file=self.outf, short=short, versioned=versioned)
  File "/usr/lib/python2.4/site-packages/bzrlib/status.py", line 143, in show_tree_status
    wt.unlock()
  File "/usr/lib/python2.4/site-packages/bzrlib/workingtree_4.py", line 1132, in unlock
    self._dirstate.save()
  File "/usr/lib/python2.4/site-packages/bzrlib/dirstate.py", line 2070, in save
    self._lock_token = self._lock_token.restore_read_lock()
  File "/usr/lib/python2.4/site-packages/bzrlib/lock.py", line 244, in restore_read_lock
    self._clear_f()
  File "/usr/lib/python2.4/site-packages/bzrlib/lock.py", line 73, in _clear_f
    self.f.close()
IOError: [Errno 5] Input/output error

0.271 return code 3