I created bar shared repo, branched lp:percona-server, lp:percona-server/5.5 and lp:percona-xtrabackup. While branching the last one I got following:

$ bzr branch lp:percona-xtrabackup
bzr: ERROR: bzrlib.errors.BzrCheckError: Internal check failed: Cannot add revision(s) to repository: missing referenced chk root keys: [StaticTuple('sha1:3cbc15851d82ad932e73ba8b79db765e0e280b75',)].Run 'bzr reconcile --canonicalize-chks' on the affected repository.

Traceback (most recent call last):
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/commands.py", line 930, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/commands.py", line 1121, in run_bzr
    ret = run(*run_argv)
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/commands.py", line 673, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/commands.py", line 697, in run
    return self._operation.run_simple(*args, **kwargs)
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/cleanup.py", line 136, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/cleanup.py", line 166, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/builtins.py", line 1507, in run
    source_branch=br_from)
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/bzrdir.py", line 367, in sprout
    create_tree_if_local=create_tree_if_local)
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/cleanup.py", line 132, in run
    self.cleanups, self.func, self, *args, **kwargs)
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/cleanup.py", line 166, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/bzrdir.py", line 417, in _sprout
    result_repo.fetch(source_repository, fetch_spec=fetch_spec)
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/vf_repository.py", line 1268, in fetch
    find_ghosts=find_ghosts, fetch_spec=fetch_spec)
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/decorators.py", line 218, in write_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/vf_repository.py", line 2585, in fetch
    find_ghosts=find_ghosts)
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/fetch.py", line 77, in __init__
    self.__fetch()
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/fetch.py", line 104, in __fetch
    self._fetch_everything_for_search(search_result)
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/fetch.py", line 132, in _fetch_everything_for_search
    stream, from_format, [])
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/vf_repository.py", line 2051, in insert_stream
    hint = self.target_repo.commit_write_group()
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/repository.py", line 633, in commit_write_group
    result = self._commit_write_group()
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/repofmt/pack_repo.py", line 1727, in _commit_write_group
    hint = self._pack_collection._commit_write_group()
  File "/usr/local/Cellar/bazaar/2.6.0/libexec/bzrlib/repofmt/pack_repo.py", line 1607, in _commit_write_group
    "Cannot add revision(s) to repository: " + problems_summary)
BzrCheckError: Internal check failed: Cannot add revision(s) to repository: missing referenced chk root keys: [StaticTuple('sha1:3cbc15851d82ad932e73ba8b79db765e0e280b75',)].Run 'bzr reconcile --canonicalize-chks' on the affected repository.

bzr 2.6.0 on python 2.7.5 (Darwin-13.3.0-x86_64-i386-64bit)
arguments: ['/usr/local/bin/bzr', 'branch', 'lp:percona-xtrabackup']
plugins: bash_completion[2.6.0], changelog_merge[2.6.0], grep[2.6.0],
    launchpad[2.6.0], netrc_credential_store[2.6.0], news_merge[2.6.0],
    po_merge[2.6.0], weave_fmt[2.6.0]
encoding: 'utf-8', fsenc: 'utf-8', lang: 'en_US.UTF-8'

*** Bazaar has encountered an internal error.  This probably indicates a
    bug in Bazaar.  You can help us fix it by filing a bug report at
        https://bugs.launchpad.net/bzr/+filebug
    including this traceback and a description of the problem.

Should we run 'bzr reconcile --canonicalize-chks' on lp:percona-xtrabackup as error log suggests?