Results of the verification test:
1. Reinstalled 14.04 with disabled trusty-proposed repository.
2. Performed openstack installation as before.
3. Reproduced the bug.
4. Activated the proposed repository and performed aptitude update.
5. Upgraded ceilometer packages using this command: "aptitude install ceilometer-agent-central ceilometer-api ceilometer-collector ceilometer-common python-ceilometer" (avoiding full upgrade, to verify the python-happybase bug later on [https://bugs.launchpad.net/ubuntu/+source/swift/+bug/1317381])
6. Tried to start swift-proxy, the output of the logfile is:
No proxy-server running
Starting proxy-server...(/etc/swift/proxy-server.conf)
Traceback (most recent call last):
  File "/usr/bin/swift-proxy-server", line 23, in <module>
    sys.exit(run_wsgi(conf_file, 'proxy-server', default_port=8080, **options))
  File "/usr/lib/python2.7/dist-packages/swift/common/wsgi.py", line 389, in run_wsgi
    loadapp(conf_path, global_conf=global_conf)
  File "/usr/lib/python2.7/dist-packages/swift/common/wsgi.py", line 316, in loadapp
    ctx = loadcontext(loadwsgi.APP, conf_file, global_conf=global_conf)
  File "/usr/lib/python2.7/dist-packages/swift/common/wsgi.py", line 307, in loadcontext
    global_conf=global_conf)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 296, in loadcontext
    global_conf=global_conf)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 320, in _loadconfig
    return loader.get_context(object_type, name, global_conf)
  File "/usr/lib/python2.7/dist-packages/swift/common/wsgi.py", line 59, in get_context
    object_type, name=name, global_conf=global_conf)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 450, in get_context
    global_additions=global_additions)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 562, in _pipeline_app_context
    for name in pipeline[:-1]]
  File "/usr/lib/python2.7/dist-packages/swift/common/wsgi.py", line 59, in get_context
    object_type, name=name, global_conf=global_conf)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 454, in get_context
    section)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 476, in _context_from_use
    object_type, name=use, global_conf=global_conf)
  File "/usr/lib/python2.7/dist-packages/swift/common/wsgi.py", line 59, in get_context
    object_type, name=name, global_conf=global_conf)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 406, in get_context
    global_conf=global_conf)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 296, in loadcontext
    global_conf=global_conf)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 328, in _loadegg
    return loader.get_context(object_type, name, global_conf)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 620, in get_context
    object_type, name=name)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 640, in find_egg_entry_point
    pkg_resources.require(self.spec)
  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 725, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 632, in resolve
    raise VersionConflict(dist,req) # XXX put more info here
pkg_resources.VersionConflict: (happybase 0.7 (/usr/lib/python2.7/dist-packages), Requirement.parse('happybase>=0.5,!=0.7'))

This refers to the happybase-related bug above.

The proposed package seems to fix the original issue. Proceeding further with happybase now.