OK, this problem affects not only uncommit. After the weird commit message going to branch.conf there is no way to work with the branch at all. I've reproduced it with simply branching the same lp project and replacing default branch.conf with supplied by bug reporter. I have the same traceback but now you don't know that qbzr is the suspect:

C:\Temp\bug-710410\sahana-eden>bzr info
bzr: ERROR: bzrlib.util.configobj.configobj.ConfigObjError: Parsing failed with several errors.
First error at line 155.

Traceback (most recent call last):
  File "bzrlib\commands.pyo", line 923, in exception_to_return_code
  File "bzrlib\commands.pyo", line 1123, in run_bzr
  File "bzrlib\commands.pyo", line 691, in run_argv_aliases
  File "bzrlib\commands.pyo", line 710, in run
  File "bzrlib\cleanup.pyo", line 135, in run_simple
  File "bzrlib\cleanup.pyo", line 165, in _do_with_cleanups
  File "bzrlib\commands.pyo", line 1138, in ignore_pipe
  File "bzrlib\builtins.pyo", line 1495, in run
  File "bzrlib\info.pyo", line 324, in show_bzrdir_info
  File "bzrlib\bzrdir.pyo", line 1447, in open_workingtree
  File "bzrlib\workingtree.pyo", line 3119, in open
  File "bzrlib\workingtree_4.pyo", line 1499, in _open
  File "bzrlib\bzrdir.pyo", line 1430, in open_branch
  File "bzrlib\branch.pyo", line 2098, in open
  File "bzrlib\branch.pyo", line 2830, in __init__
  File "bzrlib\branch.pyo", line 2440, in __init__
  File "bzrlib\branch.pyo", line 98, in __init__
  File "bzrlib\branch.pyo", line 2814, in _open_hook
  File "bzrlib\branch.pyo", line 3041, in get_stacked_on_url
  File "bzrlib\branch.pyo", line 1157, in _get_config_location
  File "bzrlib\config.pyo", line 197, in get_user_option
  File "bzrlib\config.pyo", line 1021, in _get_user_option
  File "bzrlib\config.pyo", line 529, in _get_user_option
  File "bzrlib\config.pyo", line 1253, in _get_parser
  File "bzrlib\config.pyo", line 1786, in _get_configobj
  File "bzrlib\config.pyo", line 149, in ConfigObj
  File "bzrlib\util\configobj\configobj.pyo", line 1223, in __init__
  File "bzrlib\util\configobj\configobj.pyo", line 1306, in _load
ConfigObjError: Parsing failed with several errors.
First error at line 155.

bzr 2.3b5 on python 2.6.6 (Windows-XP-5.1.2600-SP3)
arguments: ['C:\\Program Files\\Bazaar\\bzr.EXE', 'info']
encoding: 'cp1251', fsenc: 'mbcs', lang: None
plugins:
  acad                 C:\work\Bazaar\plugins\acad [0.8.0]
  bzrtools             C:\Program Files\Bazaar\plugins\bzrtools [2.3.0]
  colo                 C:\Program Files\Bazaar\plugins\colo [0.2.0]
  explorer             C:\Program Files\Bazaar\plugins\explorer [1.1.3dev]
  format1              C:\work\Bazaar\plugins\format1 [unknown]
  launchpad            C:\Program Files\Bazaar\plugins\launchpad [2.3b5]
  qbzr                 C:\Program Files\Bazaar\plugins\qbzr [0.20.0dev1]
  rewrite              C:\Program Files\Bazaar\plugins\rewrite [0.6.2dev]
  scmproj              C:\work\Bazaar\plugins\scmproj [0.6.1]
  x_bit                C:\work\Bazaar\plugins\x_bit [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.

So, the problem in the underlying ConfigObj: it can write bad conf file and unable to read it back.
I'm not quite understand how to fix it in the QBzr.