caching writes to pack repository causes ShortReadvError on pushing stacked branch

This branch to has been committed to by all sorts of pre-release versions of bzr, so it might well be broken in subtle ways, but still:

mwh@grond:manual-stacking-on-launchpad-branches-bug-272372$ bzr push
Using saved push location: bzr+ssh://bazaar.launchpad.net/~mwhudson/launchpad/manual-stacking-on-launchpad-branches-bug-272372
bzr: ERROR: bzrlib.errors.ShortReadvError: readv() read 0 bytes rather than 185 bytes at 25704 for "00/00/71/72/.bzr/repository/upload/iry9c2gg0oqyzllil702.pack"

Traceback (most recent call last):
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 893, in run_bzr_catch_errors
    return run_bzr(argv)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 839, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 539, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.5/site-packages/bzrlib/builtins.py", line 913, in run
    use_existing_dir=use_existing_dir)
  File "/usr/lib/python2.5/site-packages/bzrlib/push.py", line 162, in _show_push_branch
    stop_revision=revision_id)
  File "/usr/lib/python2.5/site-packages/bzrlib/decorators.py", line 138, in read_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/python2.5/site-packages/bzrlib/branch.py", line 1799, in push
    _override_hook_source_branch=_override_hook_source_branch)
  File "/usr/lib/python2.5/site-packages/bzrlib/branch.py", line 2508, in _run_with_write_locked_target
    result = callable(*args, **kwargs)
  File "/usr/lib/python2.5/site-packages/bzrlib/branch.py", line 1838, in _push_with_bound_branches
    result = self._basic_push(target, overwrite, stop_revision)
  File "/usr/lib/python2.5/site-packages/bzrlib/branch.py", line 1861, in _basic_push
    graph=graph)
  File "/usr/lib/python2.5/site-packages/bzrlib/decorators.py", line 192, in write_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/python2.5/site-packages/bzrlib/remote.py", line 1768, in update_revisions
    self.fetch(other, stop_revision)
  File "/usr/lib/python2.5/site-packages/bzrlib/decorators.py", line 192, in write_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/python2.5/site-packages/bzrlib/branch.py", line 286, in fetch
    pb=nested_pb)
  File "/usr/lib/python2.5/site-packages/bzrlib/remote.py", line 838, in fetch
    return inter.fetch(revision_id=revision_id, pb=pb, find_ghosts=find_ghosts)
  File "/usr/lib/python2.5/site-packages/bzrlib/decorators.py", line 192, in write_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/python2.5/site-packages/bzrlib/repository.py", line 2848, in fetch
    pb, find_ghosts, set_cache_size)
  File "/usr/lib/python2.5/site-packages/bzrlib/fetch.py", line 118, in __init__
    self.__fetch()
  File "/usr/lib/python2.5/site-packages/bzrlib/fetch.py", line 148, in __fetch
    self._fetch_everything_for_search(search, pp)
  File "/usr/lib/python2.5/site-packages/bzrlib/fetch.py", line 191, in _fetch_everything_for_search
    not self.to_repository._fetch_uses_deltas))
  File "/usr/lib/python2.5/site-packages/bzrlib/knit.py", line 1443, in insert_record_stream
    record, record.get_bytes_as(record.storage_kind)))
  File "/usr/lib/python2.5/site-packages/bzrlib/knit.py", line 229, in get_bytes
    [compression_parent], 'unordered', True).next()
  File "/usr/lib/python2.5/site-packages/bzrlib/knit.py", line 1185, in get_record_stream
    ordering, include_delta_closure):
  File "/usr/lib/python2.5/site-packages/bzrlib/knit.py", line 1281, in _get_remaining_record_stream
    text_map, _ = self._get_content_maps(keys, non_local)
  File "/usr/lib/python2.5/site-packages/bzrlib/knit.py", line 1005, in _get_content_maps
    record_map = self._get_record_map(keys, allow_missing=True)
  File "/usr/lib/python2.5/site-packages/bzrlib/knit.py", line 1133, in _get_record_map
    for key, record, digest in self._read_records_iter(records):
  File "/usr/lib/python2.5/site-packages/bzrlib/knit.py", line 1673, in _read_records_iter
    izip(iter(needed_records), raw_data):
  File "/usr/lib/python2.5/site-packages/bzrlib/knit.py", line 2540, in get_raw_records
    for names, read_func in reader.iter_records():
  File "/usr/lib/python2.5/site-packages/bzrlib/pack.py", line 253, in iter_records
    self._read_format()
  File "/usr/lib/python2.5/site-packages/bzrlib/pack.py", line 294, in _read_format
    format = self._read_line()
  File "/usr/lib/python2.5/site-packages/bzrlib/pack.py", line 221, in _read_line
    line = self._source.readline()
  File "/usr/lib/python2.5/site-packages/bzrlib/pack.py", line 185, in readline
    self._next()
  File "/usr/lib/python2.5/site-packages/bzrlib/pack.py", line 172, in _next
    length, data = self.readv_result.next()
  File "/usr/lib/python2.5/site-packages/bzrlib/transport/remote.py", line 360, in _readv
    self._translate_error(err, relpath)
  File "/usr/lib/python2.5/site-packages/bzrlib/transport/remote.py", line 425, in _translate_error
    remote._translate_error(err, path=relpath)
  File "/usr/lib/python2.5/site-packages/bzrlib/remote.py", line 1886, in _translate_error
    args[0], int(args[1]), int(args[2]), int(args[3]))
ShortReadvError: readv() read 0 bytes rather than 185 bytes at 25704 for "00/00/71/72/.bzr/repository/upload/iry9c2gg0oqyzllil702.pack"

bzr 1.11dev on python 2.5.2 (linux2)
arguments: ['/usr/bin/bzr', 'push']
encoding: 'UTF-8', fsenc: 'UTF-8', lang: 'en_NZ.UTF-8'
plugins:
  avahi /home/mwh/.bazaar/plugins/avahi [0.3dev]
  bpm /home/mwh/.bazaar/plugins/bpm [unknown]
  dbus /home/mwh/.bazaar/plugins/dbus [unknown]
  fastimport /home/mwh/.bazaar/plugins/fastimport [unknown]
  gtk /home/mwh/.bazaar/plugins/gtk [0.95.0.dev.1]
  launchpad /usr/lib/python2.5/site-packages/bzrlib/plugins/launchpad [unknown]
  loom /home/mwh/.bazaar/plugins/loom [1.4dev]
  lpreview /home/mwh/.bazaar/plugins/lpreview [unknown]
  merged /home/mwh/.bazaar/plugins/merged [unknown]
  pqm /home/mwh/.bazaar/plugins/pqm [1.4dev]
  pybloom /home/mwh/.bazaar/plugins/pybloom [unknown]
  search /home/mwh/.bazaar/plugins/search [1.6dev]
  service /home/mwh/.bazaar/plugins/service [unknown]
*** Bazaar has encountered an internal error.
    Please report a bug at https://bugs.launchpad.net/bzr/+filebug
    including this traceback, and a description of what you
    were doing when the error occurred.