bzr branch fails on a ssh mount of remote ext4 fs with Error 95 Operation Not Supported

I'm using a VM, running 12.10, upgraded from 12.04.1 (server). Using a bzr checkout dir on the VM and mounting that locally on the host with SSH from /home/USER/.gvfs/home/VMUSER/work/maas, symlinked to /home/USER/work/maas, then running bzr branch --switch on the host, while in the symlink dir. I get an Error 95 Operation not supported. And looking at the traceback in the log, it seems the fs reports erroneously supporting fdatasync, but actually fails later when bzr tries to do it.

Running the same command on the VM locally works.

Traceback (most recent call last):
  File ".../bzrlib/commands.py", line 920, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File ".../bzrlib/commands.py", line 1131, in run_bzr
    ret = run(*run_argv)
  File ".../bzrlib/commands.py", line 673, in run_argv_aliases
    return self.run(**all_cmd_args)
  File ".../bzrlib/commands.py", line 695, in run
    return self._operation.run_simple(*args, **kwargs)
  File ".../bzrlib/cleanup.py", line 136, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File ".../bzrlib/cleanup.py", line 166, in _do_with_cleanups
    result = func(*args, **kwargs)
  File ".../bzrlib/builtins.py", line 1493, in run
    source_branch=br_from)
  File ".../bzrlib/bzrdir.py", line 366, in sprout
    create_tree_if_local=create_tree_if_local)
  File ".../bzrlib/cleanup.py", line 132, in run
    self.cleanups, self.func, self, *args, **kwargs)
  File ".../bzrlib/cleanup.py", line 166, in _do_with_cleanups
    result = func(*args, **kwargs)
  File ".../bzrlib/bzrdir.py", line 416, in _sprout
    result_repo.fetch(source_repository, fetch_spec=fetch_spec)
  File ".../bzrlib/vf_repository.py", line 1267, in fetch
    find_ghosts=find_ghosts, fetch_spec=fetch_spec)
  File ".../bzrlib/decorators.py", line 218, in write_locked
    result = unbound(self, *args, **kwargs)
  File ".../bzrlib/vf_repository.py", line 2584, in fetch
    find_ghosts=find_ghosts)
  File ".../bzrlib/fetch.py", line 77, in __init__
    self.__fetch()
  File ".../bzrlib/fetch.py", line 104, in __fetch
    self._fetch_everything_for_search(search_result)
  File ".../bzrlib/fetch.py", line 132, in _fetch_everything_for_search
    stream, from_format, [])
  File ".../bzrlib/vf_repository.py", line 2050, in insert_stream
    hint = self.target_repo.commit_write_group()
  File ".../bzrlib/repository.py", line 633, in commit_write_group
    result = self._commit_write_group()
  File ".../bzrlib/repofmt/pack_repo.py", line 1727, in _commit_write_group
    hint = self._pack_collection._commit_write_group()
  File ".../bzrlib/repofmt/pack_repo.py", line 1612, in _commit_write_group
    self._new_pack.finish()
  File ".../bzrlib/repofmt/pack_repo.py", line 496, in finish
    want_fdatasync=self._pack_collection.config_stack.get('repository.fdatasync'))
  File ".../bzrlib/transport/__init__.py", line 237, in close
    self.fdatasync()
  File ".../bzrlib/transport/__init__.py", line 268, in fdatasync
    self.file_handle.flush()
IOError: [Errno 95] Operation not supported

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: bzr 2.5.1-0ubuntu2
ProcVersionSignature: Ubuntu 3.2.0-32.51-generic 3.2.30
Uname: Linux 3.2.0-32-generic x86_64
NonfreeKernelModules: fglrx
ApportVersion: 2.0.1-0ubuntu14
Architecture: amd64
Date: Mon Nov 5 11:16:01 2012
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111012)
PackageArchitecture: all
SourcePackage: bzr
UpgradeStatus: Upgraded to precise on 2012-05-03 (186 days ago)