scp:,sftp: fails collection-status, but file:/// works ok

Not sure if this is a bug that's cropped up or I'm doing something wrong. This chant (and similar) used to work all the time:

root@brit-ubtu1:~# export PASSPHRASE='*****'
root@brit-ubtu1:~# duplicity --ssh-options="-oIdentityFile=/root/.ssh/id_rsa" --archive-dir /root/.cache/duplicity collection-status scp://bick-ubtu3/mnt/backup/brit-ubtu1/home

But now it just results in:

    Local and Remote metadata are synchronized, no sync needed.
    Last full backup date: none
    Collection Status
    -----------------
    Connecting with backend: SftpBackend
    Archive dir: /root/.cache/duplicity/70dfc8d7c5fda720e18fa1924cd9314b

    Found 0 secondary backup chains.
    No backup chains with active signatures found
    No orphaned or incomplete backup sets found.
    root@brit-ubtu1:~#

I have tried clearing the cache and a few other desperate measures; no result.

However (no changes), this works fine:

    fbicknel@brit-ubtu1:~$ sudo sshfs root@bick-ubtu3:/mnt/backup/`hostname`/ b
    fbicknel@brit-ubtu1:~$ sudo ls -l b
    total 16
    drwxr-xr-x 1 root root 72 Jun 17 11:03 etc
    drwxr-xr-x 1 root root 4096 Jun 17 11:03 home
    drwxr-xr-x 1 root root 1 Jun 17 10:31 pic1
    drwxr-xr-x 1 root root 72 Jun 17 11:03 root
    fbicknel@brit-ubtu1:~$ sudo su -c "PASSPHRASE=\"`sudo cat /root/.passwords/dbackup`\" duplicity --archive-dir /root/.cache/duplicity collection-status file:///home/fbicknel/b/home"
    Synchronizing remote metadata to local cache...
    Last full backup date: Sun Jun 17 10:08:53 2012
    Collection Status
    -----------------
    Connecting with backend: LocalBackend
    Archive dir: /root/.cache/duplicity/43caa524a1b16e8aa8b3169a930e1019

    Found 0 secondary backup chains.

    Found primary backup chain with matching signature chain:
    -------------------------
    Chain start time: Sun Jun 17 10:08:53 2012
    Chain end time: Sun Jun 17 11:03:21 2012
    Number of contained backup sets: 3
    Total number of contained volumes: 83
     Type of backup set: Time: Num volumes:
                    Full Sun Jun 17 10:08:53 2012 81
             Incremental Sun Jun 17 10:44:41 2012 1
             Incremental Sun Jun 17 11:03:21 2012 1
    -------------------------
    No orphaned or incomplete backup sets found.
    fbicknel@brit-ubtu1:~$

Any idea what is going on here?

Notes:
    - Had to struggle a bit with the latest version not honoring the identity file from ssh_config, hence the -oIdentityFile command line parameter. Found that someplace else, but at least it works.
    - Tried --use-scp, but the result is the same.
    - Versions are identical on both machines:
        bick-ubtu3:~$ cat /etc/lsb-release
        DISTRIB_ID=Ubuntu
        DISTRIB_RELEASE=12.04
        DISTRIB_CODENAME=precise
        DISTRIB_DESCRIPTION="Ubuntu 12.04 LTS"
        bick-ubtu3:~$ duplicity --version
        duplicity 0.6.18
        bick-ubtu3:~$
    - Backing up works fine - it produced the backup set(s) shown above. verfiy doesn't work and collection-status doesn't work.