ValueError: InvalidMode ('r+w')

From http://pastebin.ubuntu.com/635284/ you can see how there is this ValueError is raised when trying to upload a file:

2011-06-29 18:46:27,161 - ubuntuone.SyncDaemon.ActionQueue - ERROR - Upload share:'' node:'8648af51-8a96-4dcc-9985-435a76ce3f59' Upload(share_id="''", hash="'sha1:68001fffab47ba467e9fa15f3d7c688179c75575'", running='False', node_id="'8648af51-8a96-4dcc-9985-435a76ce3f59'", upload_id='None', crc32='4065222833L', path="u'\\\\\\\\?\\\\C:\\\\Users\\\\Test\\\\Ubuntu One\\\\yadda\\\\ugly\\u200b\\u203d\\u200b.png'", previous_hash="'sha1:366314b9b80357a8d070e652d69dc8099b677165'", size='132') Error running the command: Invalid mode ('r+w') (traceback follows)
Traceback (most recent call last):
  File "C:\Users\Test\src\ubuntuone-client\ubuntuone\syncdaemon\action_queue.py", line 1287, in go
    yield self.run()
ValueError: Invalid mode ('r+w')
2011-06-29 18:46:27,395 - ubuntuone.SyncDaemon.ActionQueue - DEBUG - Upload share:'' node:'8648af51-8a96-4dcc-9985-435a76ce3f59' Upload(share_id="''", hash="'sha1:68001fffab47ba467e9fa15f3d7c688179c75575'", running='False', node_id="'8648af51-8a96-4dcc-9985-435a76ce3f59'", upload_id='None', crc32='4065222833L', path="u'\\\\\\\\?\\\\C:\\\\Users\\\\Test\\\\Ubuntu One\\\\yadda\\\\ugly\\u200b\\u203d\\u200b.png'", previous_hash="'sha1:366314b9b80357a8d070e652d69dc8099b677165'", size='132') pathlock releasing (u'', u'', u'?', u'C:', u'Users', u'Test', u'Ubuntu One', u'yadda', u'ugly\u200b\u203d\u200b.png'); remaining: 1

Is not clear to me if this is a windows-only bug.