incompatible with 2a repositories

$ bzr branch http://bzr.savannah.gnu.org/r/grub/trunk/grub/
Branched 1855 revision(s).

$ bzr branch https://alioth.debian.org/anonscm/bzr/pkg-grub/trunk/grub/ debian
Branched 820 revision(s).

$ cd grub/

$ bzr merge-into ../debian/
bzr: ERROR: exceptions.AttributeError: 'CHKInventory' object has no attribute '_byid'

Traceback (most recent call last):
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 842, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 1037, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 654, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/home/rmh/.bazaar/plugins/merge_into/__init__.py", line 47, in run
    conflicts = merge_into.merge_into_helper(location, subdir)
  File "/home/rmh/.bazaar/plugins/merge_into/merge_into.py", line 174, in merge_into_helper
    conflicts = merger.do_merge()
  File "/usr/lib/python2.5/site-packages/bzrlib/merge.py", line 507, in do_merge
    merge = self.make_merger()
  File "/usr/lib/python2.5/site-packages/bzrlib/merge.py", line 475, in make_merger
    **kwargs)
  File "/home/rmh/.bazaar/plugins/merge_into/merge_into.py", line 146, in __call__
    return self._merge_type(*args, **kwargs)
  File "/home/rmh/.bazaar/plugins/merge_into/merge_into.py", line 93, in __init__
    self._fix_other_tree(this_tree, other_tree)
  File "/home/rmh/.bazaar/plugins/merge_into/merge_into.py", line 109, in _fix_other_tree
    del other_tree.inventory._byid[root_ie.file_id]
AttributeError: 'CHKInventory' object has no attribute '_byid'

bzr 2.0.1 on python 2.5.4 (Linux-2.6.26-libre2-2-amd64-x86_64-with-debian-squeeze-sid)
arguments: ['/usr/bin/bzr', 'merge-into', '../debian/']
encoding: 'UTF-8', fsenc: 'UTF-8', lang: 'ca_AD.UTF-8'
plugins:
  bzrtools /usr/lib/python2.5/site-packages/bzrlib/plugins/bzrtools [2.0.1]
  cia /usr/lib/python2.5/site-packages/bzrlib/plugins/cia [1.0.0dev]
  cvsps_import /usr/lib/python2.5/site-packages/bzrlib/plugins/cvsps_import [unknown]
  fastimport /home/rmh/.bazaar/plugins/fastimport [0.9.0dev]
  git /usr/lib/python2.5/site-packages/bzrlib/plugins/git [0.4.1]
  launchpad /usr/lib/python2.5/site-packages/bzrlib/plugins/launchpad [2.0.1]
  merge_into /home/rmh/.bazaar/plugins/merge_into [unknown]
  netrc_credential_store /usr/lib/python2.5/site-packages/bzrlib/plugins/netrc_credential_store [2.0.1]
  rebase /usr/lib/python2.5/site-packages/bzrlib/plugins/rebase [0.5.4]
  svn /usr/lib/python2.5/site-packages/bzrlib/plugins/svn [1.0.0]

*** 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.