bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack fails on some architectures

See e.g. https://buildd.debian.org/status/fetch.php?pkg=bzr&arch=i386&ver=2.4.0~beta4-4&stamp=1308860424:

11.298 creating repository in file:///tmp/testbzr-ziA_mK.tmp/bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack/work/a/.bzr/.
11.314 creating branch <bzrlib.branch.BzrBranchFormat7 object at 0xd15cf8c> in file:///tmp/testbzr-ziA_mK.tmp/bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack/work/a/
11.361 trying to create missing lock '/tmp/testbzr-ziA_mK.tmp/bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack/work/a/.bzr/checkout/dirstate'
11.361 opening working tree '/tmp/testbzr-ziA_mK.tmp/bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack/work/a'
11.426 preparing to commit
    INFO Committing to: /tmp/testbzr-ziA_mK.tmp/bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack/work/a/
11.442 Selecting files for commit with filter None
    INFO added hello
    INFO Committed revision 1.
11.508 Committed revid <email address hidden> as revno 1.
11.558 preparing to commit
    INFO Committing to: /tmp/testbzr-ziA_mK.tmp/bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack/work/a/
11.566 Selecting files for commit with filter None
    INFO added goodbye
    INFO Committed revision 2.
11.599 Committed revid <email address hidden> as revno 2.
11.603 run bzr: ['branch', 'a', 'b']
11.603 bazaar version: 2.4b4
11.603 bzr arguments: [u'branch', u'a', u'b']
11.608 encoding stdout as sys.stdout encoding 'ANSI_X3.4-1968'
11.616 opening working tree '/tmp/testbzr-ziA_mK.tmp/bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack/work/a'
11.639 opening working tree '/tmp/testbzr-ziA_mK.tmp/bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack/work/a'
11.665 creating repository in file:///tmp/testbzr-ziA_mK.tmp/bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack/work/b/.bzr/.
11.685 Using fetch logic to copy between CHKInventoryRepository('file:///tmp/testbzr-ziA_mK.tmp/bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack/work/a/.bzr/repository/')(RepositoryFormat2a()) and CHKInventoryRepository('file:///tmp/testbzr-ziA_mK.tmp/bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack/work/b/.bzr/repository/')(RepositoryFormat2a())
11.685 fetching: <PendingAncestryResult heads:frozenset(['<email address hidden>']) repo:CHKInventoryRepository('file:///tmp/testbzr-ziA_mK.tmp/bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack/work/a/.bzr/repository/')>
11.779 creating branch <bzrlib.branch.BzrBranchFormat7 object at 0x969138c> in file:///tmp/testbzr-ziA_mK.tmp/bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack/work/b/
11.811 created new branch BzrBranch7(file:///tmp/testbzr-ziA_mK.tmp/bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack/work/b/)
11.816 trying to create missing lock '/tmp/testbzr-ziA_mK.tmp/bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack/work/b/.bzr/checkout/dirstate'
11.816 opening working tree '/tmp/testbzr-ziA_mK.tmp/bzrlib.tests.blackbox.test_branch.TestBranch.test_branch_broken_pack/work/b'
    INFO Branched 2 revision(s).
11.868 errors:
'Branched 2 revision(s).\n'
11.885 opening working tree '/tmp/testbzr-ziA_mK.tmp'
------------
Text attachment: traceback
------------
Traceback (most recent call last):
  File "/usr/lib/python2.6/dist-packages/testtools/runtest.py", line 169, in _run_user
    return fn(*args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/testtools/testcase.py", line 540, in _run_test_method
    return self._get_test_method()()
  File "/build/buildd-bzr_2.4.0~beta4-4-i386-gWyWkA/bzr-2.4.0~beta4/build/lib.linux-i686-2.6/bzrlib/tests/blackbox/test_branch.py", line 73, in test_branch_broken_pack
    'branch a b', retcode=3)
AssertionError: Unexpected return code
not equal:
a = 3
b = 0