Adding a note to mention that this bug makes is quite difficult to use the PPA with Github repositories. I wanted to try to build my own .deb for Jabref, so I started by trying to import the code from the Jabref github pages. Here is where I got to:
https://code.launchpad.net/~jdpipe/jabref/debian

However, when importing from Github, there is an error from Launchpad, specifically from "/srv/importd.launchpad.net/production/launchpad-rev-18169/bzrplugins/git/mapping.py" line 334, where a 'gpgsig' commit field seems to have triggered some kind of error.

A little surprised by this... surely other people are importing code from Github?

Cheers
JP

2016-08-03 02:07:49 INFO    Starting job.
2016-08-03 02:07:49 INFO    Getting exising bzr branch from central store.
2016-08-03 02:07:50 INFO    [chan bzr SocketAsChannelAdapter] Opened sftp connection (server version 3)
2016-08-03 02:07:50 INFO    [chan bzr SocketAsChannelAdapter] Opened sftp connection (server version 3)
2016-08-03 02:07:50 INFO    285 bytes transferred
2016-08-03 02:07:51 INFO    Importing branch.
2016-08-03 02:07:53 INFO    Counting objects: 118432, done. 0
2016-08-03 02:08:53 INFO    68240614 bytes transferred | Compressing objects 3/3
2016-08-03 02:09:05 INFO    finding revisions to fetch:generating index 0/118432
2016-08-03 02:09:26 INFO    finding revisions to fetch:generating index 0/118432
2016-08-03 02:09:38 INFO    finding revisions to fetch 1/3
2016-08-03 02:09:38 INFO    
Traceback (most recent call last):
  File "/srv/importd.launchpad.net/production/launchpad-rev-18169/scripts/code-import-worker.py", line 96, in <module>
    sys.exit(script.main())
  File "/srv/importd.launchpad.net/production/launchpad-rev-18169/scripts/code-import-worker.py", line 91, in main
    return import_worker.run()
  File "/srv/importd.launchpad.net/production/launchpad-rev-18169/lib/lp/codehosting/codeimport/worker.py", line 583, in run
    return self._doImport()
  File "/srv/importd.launchpad.net/production/launchpad-rev-18169/lib/lp/codehosting/codeimport/worker.py", line 737, in _doImport
    inter_branch.fetch(limit=revision_limit)
  File "/srv/importd.launchpad.net/production/launchpad-rev-18169/bzrplugins/git/branch.py", line 722, in fetch
    self.fetch_objects(stop_revision, fetch_tags=fetch_tags, limit=limit)
  File "/srv/importd.launchpad.net/production/launchpad-rev-18169/bzrplugins/git/branch.py", line 745, in fetch_objects
    determine_wants, self.source.mapping, limit=limit)
  File "/srv/importd.launchpad.net/production/launchpad-rev-18169/bzrplugins/git/fetch.py", line 718, in fetch_objects
    limit)
  File "/srv/importd.launchpad.net/production/launchpad-rev-18169/bzrplugins/git/fetch.py", line 484, in import_git_objects
    mapping.revision_id_foreign_to_bzr)
  File "/srv/importd.launchpad.net/production/launchpad-rev-18169/bzrplugins/git/mapping.py", line 334, in import_commit
    raise UnknownCommitExtra(commit, [item[0] for item in commit.extra])
bzrlib.plugins.git.errors.UnknownCommitExtra: Unknown extra fields in <Commit e0380b795f649afaf6cd708abc5bf2680c8a01c0>: ['gpgsig'].
Import failed:
Traceback (most recent call last):
Failure: twisted.internet.error.ProcessTerminated: A process has ended with a probable error condition: process ended with exit code 1.