Sortedness problems with MultiIndex
Take this example:

   arrays = [['bar', 'bar', 'baz', 'baz', 'qux', 'qux', 'foo', 'foo'],
             ['one', 'two', 'one', 'two', 'one', 'two', 'one', 'two']]
   tuples = zip(*arrays)
   tuples
   index = MultiIndex.from_tuples(tuples)
   s = Series(randn(8), index=index)

This does not yield the expected result:

   s['qux']
