Crash during restore: "assert ropath.index == (), ropath.index"

Duplicity version: 0.6.15
Python version: 2.7.2+
OS: Ubuntu 11.10
Target filesystem: Linux (Synology NAS, via sftp)

I'm experiencing a repeatable crash which manifests itself on restore, when the initial backup is interrupted and resumed. The data I use doesn't seem to matter. Steps to reproduce:

1. Create a directory of test data. Mine was around 125MiB
2. duplicity --no-encryption TestDir ssh://user@target/backup/TestDir
3. Wait until one or two tar files have been uploaded, then Ctrl-C to kill duplicity
4. duplicity --no-encryption TestDir ssh://user@target/backup/TestDir (duplicity should resume the backup where it left off; allow it to complete this time)
5. duplicity --no-encryption TestDir ssh://user@target/backup/TestDir (repeat the command a third time - note that duplicity reports a nonzero number of DeletedFiles even though the data has not changed.
6. rm -r TestDir
7. duplicity --no-encryption ssh://user@target/backup/TestDir TestDir (attempt to restore -> crash)

The crash output is as follows:

user@laptop:~$ duplicity --no-encryption ssh://user@target/backup/Test4 Test4
Local and Remote metadata are synchronized, no sync needed.
Last full backup date: Wed Feb 8 19:29:16 2012
Traceback (most recent call last):
  File "/usr/bin/duplicity", line 1359, in <module>
    with_tempdir(main)
  File "/usr/bin/duplicity", line 1342, in with_tempdir
    fn()
  File "/usr/bin/duplicity", line 1276, in main
    restore(col_stats)
  File "/usr/bin/duplicity", line 591, in restore
    restore_get_patched_rop_iter(col_stats)):
  File "/usr/lib/python2.7/dist-packages/duplicity/patchdir.py", line 523, in Write_ROPaths
    ITR( ropath.index, ropath )
  File "/usr/lib/python2.7/dist-packages/duplicity/lazy.py", line 320, in __call__
    self.process_w_branch(index, self.root_branch, args)
  File "/usr/lib/python2.7/dist-packages/duplicity/lazy.py", line 293, in process_w_branch
    branch.start_process, args)
  File "/usr/lib/python2.7/dist-packages/duplicity/robust.py", line 37, in check_common_error
    return function(*args)
  File "/usr/lib/python2.7/dist-packages/duplicity/patchdir.py", line 545, in start_process
    assert ropath.index == (), ropath.index
AssertionError: somefile.dat

I can provide more information, log output, test data (although the data doesn't seem to matter), or test with other versions of duplicity if requested.