Once a cache_set is created the UI fails with ERROR

Once I created a cache_set the UI became unusable. I saw the following error in the regiond.log.

2015-11-24 09:19:33 [-] Error on request (83) node.set_active: 'NoneType' object has no attribute 'virtual_devices'
 Traceback (most recent call last):
   File "/usr/lib/python2.7/threading.py", line 783, in __bootstrap
     self.__bootstrap_inner()
   File "/usr/lib/python2.7/threading.py", line 810, in __bootstrap_inner
     self.run()
   File "/usr/lib/python2.7/threading.py", line 763, in run
     self.__target(*self.__args, **self.__kwargs)
   File "/usr/lib/python2.7/dist-packages/provisioningserver/utils/twisted.py", line 791, in _worker
     return super(ThreadPool, self)._worker()
 --- <exception caught here> ---
   File "/usr/lib/python2.7/dist-packages/twisted/python/threadpool.py", line 191, in _worker
     result = context.call(ctx, function, *args, **kwargs)
   File "/usr/lib/python2.7/dist-packages/twisted/python/context.py", line 118, in callWithContext
     return self.currentContext().callWithContext(ctx, func, *args, **kw)
   File "/usr/lib/python2.7/dist-packages/twisted/python/context.py", line 81, in callWithContext
     return func(*args,**kw)
   File "/usr/lib/python2.7/dist-packages/maasserver/utils/orm.py", line 501, in call_within_transaction
     return func_outside_txn(*args, **kwargs)
   File "/usr/lib/python2.7/dist-packages/maasserver/utils/orm.py", line 328, in retrier
     return func(*args, **kwargs)
   File "/usr/lib/python2.7/dist-packages/django/db/transaction.py", line 339, in inner
     return func(*args, **kwargs)
   File "/usr/lib/python2.7/dist-packages/maasserver/websockets/base.py", line 416, in set_active
     obj_data = self.get(params)
   File "/usr/lib/python2.7/dist-packages/maasserver/websockets/base.py", line 349, in get
     return self.full_dehydrate(obj)
   File "/usr/lib/python2.7/dist-packages/maasserver/websockets/base.py", line 205, in full_dehydrate
     return self.dehydrate(obj, data, for_list=for_list)
   File "/usr/lib/python2.7/dist-packages/maasserver/websockets/handlers/node.py", line 316, in dehydrate
     data["storage_layout_issues"] = obj.storage_layout_issues()
   File "/usr/lib/python2.7/dist-packages/maasserver/models/node.py", line 813, in storage_layout_issues
     if on_bcache(block_device):
   File "/usr/lib/python2.7/dist-packages/maasserver/models/node.py", line 774, in on_bcache
     for parent in obj.virtualblockdevice.get_parents():
   File "/usr/lib/python2.7/dist-packages/maasserver/models/virtualblockdevice.py", line 165, in get_parents
     if check_fs_group(block_device):
   File "/usr/lib/python2.7/dist-packages/maasserver/models/virtualblockdevice.py", line 154, in check_fs_group
     for virtual_device in fs_group.virtual_devices.all():
 exceptions.AttributeError: 'NoneType' object has no attribute 'virtual_devices'