Duplicity backup fails with "unknown error"

[CaptSaltyJack]

Contents of backup window show:

Traceback (most recent call last):
  File "/usr/bin/duplicity", line 1411, in <module>
    with_tempdir(main)
  File "/usr/bin/duplicity", line 1404, in with_tempdir
    fn()
  File "/usr/bin/duplicity", line 1338, in main
    restore(col_stats)
  File "/usr/bin/duplicity", line 632, in restore
    restore_get_patched_rop_iter(col_stats)):
  File "/usr/lib/python2.7/dist-packages/duplicity/patchdir.py", line 526, in Write_ROPaths
    for ropath in rop_iter:
  File "/usr/lib/python2.7/dist-packages/duplicity/patchdir.py", line 499, in integrate_patch_iters
    final_ropath = patch_seq2ropath( normalize_ps( patch_seq ) )
  File "/usr/lib/python2.7/dist-packages/duplicity/patchdir.py", line 466, in patch_seq2ropath
    assert len( patch_seq ) == 1, len( patch_seq )
AssertionError: 2

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: deja-dup 26.0-0ubuntu1
ProcVersionSignature: Ubuntu 3.8.0-29.42-generic 3.8.13.5
Uname: Linux 3.8.0-29-generic x86_64
ApportVersion: 2.9.2-0ubuntu8.3
Architecture: amd64
Date: Thu Sep 5 10:57:18 2013
InstallationDate: Installed on 2013-08-29 (7 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
MarkForUpload: True
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: deja-dup
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.