Comment 1 for bug 375013

This bug (or at least I think it is this bug) causes test_branch_from_trivial_stacked_branch_streaming_acceptance in bzrlib/tests/blackbox/test_branch.py to fail if you change that test to use a 2a format branch:

[...]
  File "/home/andrew/warthogs/bzr/blackbox-with-2a/bzrlib/repofmt/groupcompress_repo.py", line 984, in _get_parent_id_basename_to_file_id_pages
    self._chk_p_id_roots, uninteresting_pid_root_keys):
  File "/home/andrew/warthogs/bzr/blackbox-with-2a/bzrlib/chk_map.py", line 1608, in process
    for record, items in self._process_queues():
  File "/home/andrew/warthogs/bzr/blackbox-with-2a/bzrlib/chk_map.py", line 1578, in _flush_new_queue
    for record, _, p_refs, items in self._read_nodes_from_store(refs):
  File "/home/andrew/warthogs/bzr/blackbox-with-2a/bzrlib/chk_map.py", line 1461, in _read_nodes_from_store
    raise errors.NoSuchRevision(self._store, record.key)
NoSuchRevision: <bzrlib.groupcompress.GroupCompressVersionedFiles object at 0x9db090c> has no revision ('sha1:a4526a70993d853ef740978187ef5479fb179fe9',)

If we change the default format to 2a, as we are planning to do quite soon, then we'll have to do something about this test failure.