Duplicity hangs trying to upload files to remote server

[Maintainer note: this thread kinda got hijacked by the maybe-related, maybe-not-related Duplicity problem mentioned in comments below. This OP is left as an archeological site. Sorry OP.]

I can connect to the host without issues but command execution doesn't work as expected:

In [13]: ssh.get_transport().is_alive()
Out[13]: True

In [14]: stdin, stdout, stderr = ssh.exec_command('ls')
DEBUG:paramiko.transport:[chan 2] Max packet in: 34816 bytes
DEBUG:paramiko.transport:[chan 2] Max packet out: 32768 bytes
INFO:paramiko.transport:Secsh channel 2 opened.
DEBUG:paramiko.transport:[chan 2] Sesch channel 2 request ok

In [15]: stdout.channel.recv_ready()
Out[15]: False

In [16]: stdout.channel.exit_status_ready()
Out[16]: False

On the other hand:
In [5]: chan = ssh.invoke_shell()

In [6]: chan.send('uname')
Out[6]: 5

In [7]: chan.recv_ready()
Out[7]: True

In [8]: chan.exit_status_ready()
Out[8]: False

In [9]: chan.send('\n')
Out[9]: 1

In [10]: chan.exit_status_ready()
Out[10]: False

In [11]:

In [11]: chan.recv_ready()
Out[11]: True

In [13]: chan.recv(1024)
Out[13]: 'Last login: Sat Apr 26 04:58:23 2014 from XXX\r\r\n[USER@XXX ~]# uname\r\nLinux\r\n[USER@XXX ~]# '

So command was executed successfully but paramiko doesn't know about it.

Start with the ssh.exec_command and ssh.invoke_shell entry points shown in the report, then inspect stdout.channel behavior for the ls example. Reproduce the difference between command execution and the interactive shell, and compare recv_ready() and exit_status_ready(). Done means the reported remote command behavior is understood and corrected or clearly reproduced with a focused regression test.