Generating public link from Nautilus not possible on Ubuntu 12.04 (Precise Pangolin)

Expected behaviour: right click on file in Nautilus -> "Ubuntu One" -> "Publish". Now it should be possible to copy the public link.

Actual behaviour: right click on file in Nautilus -> "Ubuntu One" -> "Publish". Now I get the notification "a file is no longer published".

These are the error messages from syncdaemon.log:

2013-07-18 18:22:37,468 - ubuntuone.SyncDaemon.EQ - ERROR - Error encountered while handling: AQ_CHANGE_PUBLIC_ACCESS_OK in <ubuntuone.eventlog.zg_listener.ZeitgeistListener object at 0x3252110>
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/ubuntuone-client/ubuntuone/syncdaemon/event_queue.py", line 316, in _dispatch
    method(**kwargs)
  File "/usr/lib/python2.7/dist-packages/ubuntuone-client/ubuntuone/eventlog/zg_listener.py", line 508, in handle_AQ_CHANGE_PUBLIC_ACCESS_OK
    self.log_unpublishing(share_id, node_id, is_public, public_url)
  File "/usr/lib/python2.7/dist-packages/ubuntuone-client/ubuntuone/eventlog/zg_listener.py", line 537, in log_unpublishing
    public_url)
  File "/usr/lib/python2.7/dist-packages/ubuntuone-client/ubuntuone/eventlog/zg_listener.py", line 290, in get_mime_and_interpretation_for_filepath
    mime, encoding = mimetypes.guess_type(filepath)
  File "/usr/lib/python2.7/mimetypes.py", line 295, in guess_type
    return _db.guess_type(url, strict)
  File "/usr/lib/python2.7/mimetypes.py", line 114, in guess_type
    scheme, url = urllib.splittype(url)
  File "/usr/lib/python2.7/urllib.py", line 1070, in splittype
    match = _typeprog.match(url)
TypeError: expected string or buffer
2013-07-18 18:22:37,527 - ubuntuone.SyncDaemon.EQ - ERROR - Error encountered while handling: AQ_CHANGE_PUBLIC_ACCESS_OK in <ubuntuone.syncdaemon.interaction_interfaces.SyncdaemonEventListener object at 0x324fdd0>
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/ubuntuone-client/ubuntuone/syncdaemon/event_queue.py", line 316, in _dispatch
    method(**kwargs)
  File "/usr/lib/python2.7/dist-packages/ubuntuone-client/ubuntuone/logger.py", line 283, in inner
    res = f(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/ubuntuone-client/ubuntuone/syncdaemon/interaction_interfaces.py", line 1074, in handle_AQ_CHANGE_PUBLIC_ACCESS_OK
    self.interface.public_files.PublicAccessChanged(info)
  File "/usr/lib/python2.7/dist-packages/dbus/decorators.py", line 314, in emit_signal
    message.append(signature=signature, *args)
TypeError: Expected a string or unicode object