The good news - the firewall fix has indeed worked and poppy is now happy with sftp connections.

The bad news - I can't see an OOPSes, so why the heck is it deferring to a thread for stuff?

Here's a log from a session - there are no errors:

2011-12-22 10:38:08+0000 [KeepAliveSettingSSHServerTransport (TimeoutProtocol),28,82.71.93.254] NEW KEYS
2011-12-22 10:38:08+0000 [KeepAliveSettingSSHServerTransport (TimeoutProtocol),28,82.71.93.254] starting service ssh-userauth
2011-12-22 10:38:08+0000 [SSHService ssh-userauth on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] julian-edwards trying auth none
2011-12-22 10:38:08+0000 [SSHService ssh-userauth on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] julian-edwards trying auth publickey
2011-12-22 10:38:08+0000 [SSHService ssh-userauth on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] Starting factory <twisted.web.xmlrpc._QueryFactory instance at 0x959d998>
2011-12-22 10:38:08+0000 [QueryProtocol,client] Stopping factory <twisted.web.xmlrpc._QueryFactory instance at 0x959d998>
2011-12-22 10:38:08+0000 [SSHService ssh-userauth on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] julian-edwards trying auth publickey
2011-12-22 10:38:08+0000 [SSHService ssh-userauth on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] julian-edwards authenticated with publickey
2011-12-22 10:38:08+0000 [SSHService ssh-userauth on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] starting service ssh-connection
2011-12-22 10:38:08+0000 [SSHService ssh-userauth on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] INFO:/srv/launchpad.net/production-logs/lp_upload/poppy-sftp-access.log:[100225824] julian-edwards logged in.
2011-12-22 10:38:08+0000 [SSHService ssh-connection on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] got channel session request
2011-12-22 10:38:08+0000 [SSHChannel session (0) on SSHService ssh-connection on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] channel open
2011-12-22 10:38:09+0000 [SSHChannel session (0) on SSHService ssh-connection on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] unhandled request for env
2011-12-22 10:38:09+0000 [SSHChannel session (0) on SSHService ssh-connection on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] unhandled request for env
2011-12-22 10:38:09+0000 [SSHChannel session (0) on SSHService ssh-connection on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] asking for subsystem "sftp"
2011-12-22 10:38:09+0000 [SSHChannel session (0) on SSHService ssh-connection on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] {'sftp': <class lp.services.sshserver.sftp.FileTransferServer at 0x5112c50>}
2011-12-22 10:38:09+0000 [SSHChannel session (0) on SSHService ssh-connection on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] INFO:/srv/launchpad.net/production-logs/lp_upload/poppy-sftp-access.log:[100225824] julian-edwards started SFTP session.
2011-12-22 10:38:09+0000 [SSHChannel session (0) on SSHService ssh-connection on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] sending close 0
2011-12-22 10:38:09+0000 [SSHChannel session (0) on SSHService ssh-connection on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] INFO:/srv/launchpad.net/production-logs/lp_upload/poppy-sftp-access.log:[100225824] julian-edwards closed SFTP session.
2011-12-22 10:38:09+0000 [SSHChannel session (0) on SSHService ssh-connection on KeepAliveSettingSSHServerTransport (TimeoutProtocol)] INFO:poppy-sftp.Hooks:Post-processing finished
2011-12-22 10:38:09+0000 [KeepAliveSettingSSHServerTransport (TimeoutProtocol),28,xx.xx1.93.254] Got remote error, code 11
        reason: disconnected by user
2011-12-22 10:38:09+0000 [KeepAliveSettingSSHServerTransport (TimeoutProtocol),28,xx.xx.93.254] INFO:/srv/launchpad.net/production-logs/lp_upload/poppy-sftp-access.log:[100225824] julian-edwards disconnected.
2011-12-22 10:38:09+0000 [KeepAliveSettingSSHServerTransport (TimeoutProtocol),28,xx.xx.93.254] connection lost
2011-12-22 10:38:09+0000 [KeepAliveSettingSSHServerTransport (TimeoutProtocol),28,xx.xx.93.254] INFO:/srv/launchpad.net/production-logs/lp_upload/poppy-sftp-access.log:[100225824] disconnected.