bzr branch lp:bzr-difftools fails for uninitialized launchpad-login: bzr: ERROR: Revision ... not present in "KnitVersionedFiles ..."

% bzr branch lp:bzr-difftools
You have not informed bzr of your Launchpad ID, and you must do this to
write to Launchpad or access private data. See "bzr help launchpad-login".
bzr: ERROR: Revision {[('README-20060424053418-5f41d3fcc4f6e800', 'sward@localhost-20060430024014-24cd2e1ba9094916')]} not present in "KnitVersionedFiles(<bzrlib.knit._KndxIndex object at 0x8e4ac4c>, <bzrlib.knit._KnitKeyAccess object at 0x8e4ac6c>)".

Branch format seems to be 1:
% cat bzr-difftools/.bzr/branch-format
Bazaar-NG meta directory, format 1

% bzr --version
Bazaar (bzr) 2.5.1
  Python interpreter: /usr/bin/python 2.7.3
  Python standard library: /usr/lib/python2.7
  Platform: Linux-3.2.0-30-generic-pae-i686-athlon-with-Ubuntu-12.04-precise
  bzrlib: /usr/lib/python2.7/dist-packages/bzrlib
  Bazaar configuration: /home/***/.bazaar
  Bazaar log file: /home/***/.bzr.log

Same error has been also reproduced with bazaar 2.5.1 and bazaar 2.6.0dev3 on 64-bit ubuntu 12.04.

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Interestingly - the same "bzr branch lp:bzr-difftools" command works fine if launchpad-login is configured for my account (i.e. when I don't have the "You have not informed bzr of your Launchpad ID" warning).