SimilarityMatrix fails on 'a few shanks'

[nippoo]

  File "/Users/chris/anaconda/envs/klusta/lib/python2.7/site-packages/klustaviewa-0.3.0-py2.7-macosx-10.5-x86_64.egg/klustaviewa/gui/taskgraph.py", line 161, in similarity_matrix_computed_callback
    cluster_groups, target_next=target_next)
  File "/Users/chris/anaconda/envs/klusta/lib/python2.7/site-packages/klustaviewa-0.3.0-py2.7-macosx-10.5-x86_64.egg/klustaviewa/gui/taskgraph.py", line 75, in <lambda>
    return lambda *args, **kwargs: self.run(('_' + name, args, kwargs))
  File "/Users/chris/anaconda/envs/klusta/lib/python2.7/site-packages/klustaviewa-0.3.0-py2.7-macosx-10.5-x86_64.egg/klustaviewa/gui/taskgraph.py", line 63, in run
    outputs = self.run_single(action)
  File "/Users/chris/anaconda/envs/klusta/lib/python2.7/site-packages/klustaviewa-0.3.0-py2.7-macosx-10.5-x86_64.egg/klustaviewa/gui/taskgraph.py", line 52, in run_single
    return getattr(self, method)(*args, **kwargs)
  File "/Users/chris/anaconda/envs/klusta/lib/python2.7/site-packages/klustaviewa-0.3.0-py2.7-macosx-10.5-x86_64.egg/klustaviewa/gui/taskgraph.py", line 307, in _similarity_matrix_computed
    if len(matrix) == 0:
TypeError: object of type 'exceptions.IndexError' has no len()