Comment 9 for bug 1376812

This seems to be the problem (except from your log):

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/django/core/handlers/base.py", line 112, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/lib/python2.7/dist-packages/django/views/generic/base.py", line 69, in view
    return self.dispatch(request, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/django/views/generic/base.py", line 87, in dispatch
    return handler(request, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/maasserver/views/images.py", line 152, in post
    self.ubuntu_sources[0], 'ubuntu', releases, arches)
  File "/usr/lib/python2.7/dist-packages/maasserver/views/images.py", line 313, in update_source_selection
    boot_source=boot_source, os=os, release=release)
  File "/usr/lib/python2.7/dist-packages/django/db/models/manager.py", line 154, in get_or_create
    return self.get_queryset().get_or_create(**kwargs)
  File "/usr/lib/python2.7/dist-packages/django/db/models/query.py", line 373, in get_or_create
    return self.get(**lookup), False
  File "/usr/lib/python2.7/dist-packages/django/db/models/query.py", line 310, in get
    (self.model._meta.object_name, num))
MultipleObjectsReturned: get() returned more than one BootSourceSelection -- it returned 3!