Backup to ssh/sftp Backend is failing on my Raspbian (Debian Jessie)

Hi there,
I'm using Duplictiy (installed from source, Version 0.7.10) on my freshly installed Raspbian system. Duplicity in invoked by duply and basically works fine as long as I'm using my Dropbox as a target. As soon as I try to switch to a SSH target (pub key authentication), I get the following error:

Backend error detail: Traceback (most recent call last):
  File "/usr/local/bin/duplicity", line 1546, in <module>
    with_tempdir(main)
  File "/usr/local/bin/duplicity", line 1540, in with_tempdir
    fn()
  File "/usr/local/bin/duplicity", line 1375, in main
    action = commandline.ProcessCommandLine(sys.argv[1:])
  File "/usr/local/lib/python2.7/dist-packages/duplicity/commandline.py", line 1117, in ProcessCommandLine
    backup, local_pathname = set_backend(args[0], args[1])
  File "/usr/local/lib/python2.7/dist-packages/duplicity/commandline.py", line 1006, in set_backend
    globals.backend = backend.get_backend(bend)
  File "/usr/local/lib/python2.7/dist-packages/duplicity/backend.py", line 223, in get_backend
    obj = get_backend_object(url_string)
  File "/usr/local/lib/python2.7/dist-packages/duplicity/backend.py", line 209, in get_backend_object
    return factory(pu)
  File "/usr/local/lib/python2.7/dist-packages/duplicity/backends/ssh_paramiko_backend.py", line 254, in __init__
    raise BackendException("sftp negotiation failed: %s" % e)
BackendException: sftp negotiation failed: Channel closed.

BackendException: sftp negotiation failed: Channel closed.

Some googling brought me to the python-paramiko packet as the scapegoat but I have the latest version of it installed (using apt).
I also turned the verbosity level up and can see that the SSH authentication basically works, the error happens directly after the authentication.

Do you have any advice for me? Is it possible that this is a bug in Duplicity?

Thanks
Nils